Light emitting device with optical redundancy

ABSTRACT

An optically redundant light emitting device includes a light transmitting film comprising an array of coupling light-guides extending from a light emitting area defined within the light transmitting film. Each coupling lightguide is bent to form a stacked array of coupling lightguides. A first group of light sources comprising at least one light source is positioned to emit light into the stacked array of coupling lightguides, and a second group of light sources comprising at least one light source is positioned to emit light into the stacked array of coupling lightguides. A first optical path of the light emitted from the first group of light sources overlaps with a second optical path of the light from the second group of light sources in each coupling lightguide.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/368,560, entitled “Light emitting device with optical redundancy,” filed Jul. 28, 2010, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The subject matter disclosed herein generally relates to light emitting devices such as light fixtures, backlights, frontlights, light emitting signs, passive displays, and active displays and their components and method of manufacture. Light emitting devices are needed which are thinner, lighter weight, cheaper to manufacture, and scalable to large sizes.

BACKGROUND

Conventionally, in order to reduce the thickness of displays and backlights, edge-lit configurations using rigid lightguides have been used to receive light from the edge and direct it out of a larger area face. These types of light emitting devices are typically housed in relatively thick, rigid frames that do not allow for component or device flexibility and require long lead times for design changes. The volume of these devices remains large and often includes thick or large frames or bezels around the device. The thick lightguides (typically 2 millimeters (mm) and larger) limit the design configurations, production methods, and illumination modes.

The ability to further reduce the thickness and overall volume of these area light emitting devices has been limited by the ability to couple sufficient light flux into a thinner lightguide. Typical LED light sources have a light emitting area dimension of at least 1 mm, and there is often difficulty controlling the light entering, propagating through, and coupled out of the 2 mm lightguide to meet design requirements. The displays incorporating the 2 mm lightguides are typically limited to small displays such as those with a 33 centimeters (cm) diagonal or less. Many system sizes are thick due to designs that use large light sources and large input coupling optics or methods. Some systems using one lightguide per pixel (such as fiber optic based systems) require a large volume and have low alignment tolerances. In production, thin lightguides have been limited to coatings on rigid wafers for integrated optical components.

SUMMARY

In one aspect, an optically redundant light emitting device includes a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film. Each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides. A first group of light sources includes at least one light source positioned to emit light into the stacked array of coupling lightguides, and a second group of light sources includes at least one light source positioned to emit light into the stacked array of coupling lightguides. When the first group of light sources and the second group of light sources are emitting light, each coupling lightguide in the stacked array of coupling lightguides receives light emitted from the first group of light sources and light emitted from the second group of light sources. The light travels by total internal reflection through the light transmitting film to the light emitting area. The light emitted from the first group of light sources and the light emitted from the second group of light sources exit the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial luminance uniformity greater than 70%. When the first group of light sources is emitting light and the second group of light sources is not emitting light, the light emitted from the first group of light sources exits the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial luminance uniformity greater than 70%.

In another aspect, an optically redundant light emitting device includes a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film. Each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides. A first group of light sources includes at least one light source positioned to emit light into the stacked array of coupling lightguides, and a second group of light sources includes at least one light source positioned to emit light into the stacked array of coupling lightguides. A first optical path of the light emitted from the first group of light sources overlaps with a second optical path of the light from the second group of light sources in each coupling lightguide.

In another aspect, a light emitting device includes a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film wherein each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides. A first group of light sources includes at least one light source of a first color positioned to emit light into the stacked array of coupling lightguides, and a second group of light sources includes at least one light source of a second color different from the first color positioned to emit light into the stacked array of coupling lightguides. Each coupling lightguide in the stacked array of coupling lightguides is positioned to receive light emitted from the first group of light sources and light emitted from the second group of light sources. The light emitting area has a VESA 9-spot sampled spatial color non-uniformity (Δu′v′) less than 0.2 when the first group of light sources and the second group of light sources are emitting light and when only the first group of light sources is emitting light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of one embodiment of a light emitting device comprising a light input coupler disposed on one side of a lightguide.

FIG. 2 is a perspective view of one embodiment of a light input coupler with coupling lightguides folded in the −y direction.

FIG. 3 is a top view of one embodiment of a light emitting device with three light input couplers on one side of a lightguide.

FIG. 4 is a top view of one embodiment of a light emitting device with two light input couplers disposed on opposite sides of a lightguide.

FIG. 5 is a top view of one embodiment of a light emitting device with two light input couplers disposed on the same side of a lightguide wherein the optical axes of the light sources are oriented substantially toward each other.

FIG. 6 is a cross-sectional side view of one embodiment of a light emitting device with a substantially flat light input surface comprised of flat edges of a coupling lightguide disposed to receive light from a light source.

FIG. 7 is a top view of one embodiment of a backlight emitting red, green, and blue light with light input couplers disposed along three sides of the lightguide.

FIG. 8 is a cross-sectional side view of one embodiment of a light emitting device comprising a light input coupler and lightguide with a reflective optical element disposed adjacent a surface.

FIG. 9 is a cross-sectional side view of one embodiment of a display illuminated by red, green, and blue lightguides wherein the locations of the pixels of the display correspond to light emitting regions of the lightguide separated by color.

FIG. 10 is a cross-sectional side view of one embodiment of a color sequential display.

FIG. 11 is a cross-sectional side view of one embodiment of a spatial display.

FIG. 12 is a cross-sectional side view of one embodiment of a display optically coupled to a film lightguide.

FIG. 13 is a cross-sectional side view of one embodiment of a light emitting device comprising a light input coupler disposed adjacent a light source with a collimating optical element.

FIG. 14 is a top view of one embodiment of an input coupler and lightguide wherein the array of coupling lightguides has non-parallel regions.

FIG. 15 is a perspective top view of a portion of the input coupler and lightguide of FIG. 14 with the coupling lightguides folded.

FIG. 16 is a cross-sectional side view of one embodiment of a light emitting device with optical redundancy comprising two lightguides stacked in the z direction.

FIG. 17 is a cross-sectional side view of one embodiment of a light emitting device with a first light source and a second light source thermally coupled to a first thermal transfer element.

FIG. 18 is a top view of one embodiment of a light emitting device comprising coupling lightguides with a plurality of first reflective surface edges and a plurality of second reflective surface edges within each coupling lightguide.

FIG. 19 is an enlarged perspective view of the input end of the coupling lightguides of FIG. 18.

FIG. 20 is a cross-sectional side view of the coupling lightguides and light source of one embodiment of a light emitting device comprising index matching regions disposed between the core regions of the coupling lightguides.

DETAILED DESCRIPTION

The features and other details of several embodiments will now be more particularly described. It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations. The principal features can be employed in various embodiments without departing from the scope of any particular embodiment. All parts and percentages are by weight unless otherwise specified.

DEFINITIONS

“Electroluminescent sign” is defined herein a means for displaying information wherein the legend, message, image or indicia thereon is formed by or made more apparent by an electrically excitable source of illumination. This includes illuminated cards, transparencies, pictures, printed graphics, fluorescent signs, neon signs, channel letter signs, light box signs, bus-stop signs, illuminated advertising signs, EL (electroluminescent) signs, LED signs, edge-lit signs, advertising displays, liquid crystal displays, electrophoretic displays, point of purchase displays, directional signs, illuminated pictures, and other information display signs. Electroluminescent signs can be self-luminous (emissive), back-illuminated (back-lit), front illuminated (front-lit), edge-illuminated (edge-lit), waveguide-illuminated or other configurations wherein light from a light source is directed through static or dynamic means for creating images or indicia.

“Optically coupled” as defined herein refers to coupling of two or more regions or layers such that the luminance of light passing from one region to the other is not substantially reduced by Fresnel interfacial reflection losses due to differences in refractive indices between the regions. “Optical coupling” methods include methods of coupling wherein the two regions coupled together have similar refractive indices or using an optical adhesive with a refractive index substantially near or between the refractive index of the regions or layers. Examples of “optical coupling” include, without limitation, lamination using an index-matched optical adhesive, coating a region or layer onto another region or layer, or hot lamination using applied pressure to join two or more layers or regions that have substantially close refractive indices. Thermal transferring is another method that can be used to optically couple two regions of material. Forming, altering, printing, or applying a material on the surface of another material are other examples of optically coupling two materials. “Optically coupled” also includes forming, adding, or removing regions, features, or materials of a first refractive index within a volume of a material of a second refractive index such that light propagates from the first material to the second material. For example, a white light scattering ink (such as titanium dioxide in a methacrylate, vinyl, or polyurethane based binder) may be optically coupled to a surface of a polycarbonate or silicone film by inkjet printing the ink onto the surface. Similarly, a light scattering material such as titanium dioxide in a solvent applied to a surface may allow the light scattering material to penetrate or adhere in close physical contact with the surface of a polycarbonate or silicone film such that it is optically coupled to the film surface or volume.

“Lightguide” or “waveguide” refers to a region bounded by the condition that light rays propagating at an angle that is larger than the critical angle will reflect and remain within the region. In a lightguide, the light will reflect or TIR (totally internally reflect) if it the angle (a) satisfies the condition α>sin⁻¹(n₂/n₁), where n₁ is the refractive index of the medium inside the lightguide and n₂ is the refractive index of the medium outside the lightguide. Typically, n₂ is air with a refractive index of 1, however, high and low refractive index materials can be used to achieve lightguide regions. The lightguide may comprise reflective components such as reflective films, aluminized coatings, surface relief features, and other components that can re-direct or reflect light. The lightguide may also contain non-scattering regions such as substrates. Light can be incident on a lightguide region from the sides or below and surface relief features or light scattering domains, phases or elements within the region can direct light into larger angles such that it totally internally reflects or into smaller angles such that the light escapes the lightguide. The lightguide does not need to be optically coupled to all of its components to be considered as a lightguide. Light may enter from any face (or interfacial refractive index boundary) of the waveguide region and may totally internally reflect from the same or another refractive index interfacial boundary. A region can be functional as a waveguide or lightguide for purposes illustrated herein as long as the thickness is larger than the wavelength of light of interest. For example, a lightguide may be a 5 micron region or layer of a film or it may be a 3 millimeter sheet comprising a light transmitting polymer.

“In contact” and “disposed on” are used generally to describe that two items are adjacent one another such that the whole item can function as desired. This may mean that additional materials can be present between the adjacent items, as long as the item can function as desired.

A “film” as used herein refers to a thin extended region, membrane, or layer of material.

A “bend” as used herein refers to a deformation or transformation in shape by the movement of a first region of an element relative to a second region, for example. Examples of bends include the bending of a clothes rod when heavy clothes are hung on the rod or rolling up a paper document to fit it into a cylindrical mailing tube. A “fold” as used herein is a type of bend and refers to the bend or lay of one region of an element onto a second region such that the first region covers at least a portion of the second region. An example of a fold includes bending a letter and forming creases to place it in an envelope. A fold does not require that all regions of the element overlap. A bend or fold may be a change in the direction along a first direction along a surface of the object. A fold or bend may or may not have creases and the bend or fold may occur in one or more directions or planes such as 90 degrees or 45 degrees. A bend or fold may be lateral, vertical, torsional, or a combination thereof.

Light Emitting Device

In one embodiment, a light emitting device comprises a first light source, a light input coupler, a light mixing region, and a lightguide comprising a light emitting region with a light extraction feature. In one embodiment, the first light source has a first light source emitting surface, the light input coupler comprises an input surface disposed to receive light from the first light source and transmit the light through the light input coupler by total internal reflection through a plurality of coupling lightguides. In this embodiment, light exiting the coupling lightguides is re-combined and mixed in a light mixing region and directed through total internal reflection within a lightguide or lightguide region. Within the lightguide, a portion of incident light is directed within the light extracting region by light extracting features into a condition whereupon the angle of light is less than the critical angle for the lightguide and the directed light exits the lightguide through the lightguide light emitting surface.

In a further embodiment, the lightguide is a film with light extracting features below a light emitting device output surface within the film and film is separated into coupling lightguide strips which are folded such that they form a light input coupler with a first input surface formed by the collection of edges of the coupling lightguides.

In one embodiment, the light emitting device has an optical axis defined herein as the direction of peak luminous intensity for light emitting from the light emitting surface or region of the device for devices with output profiles with one peak. For optical output profiles with more than one peak and the output is symmetrical about an axis, such as with a “batwing” type profile, the optical axis of the light emitting device is the axis of symmetry of the light output. In light emitting devices with angular luminous intensity optical output profiles with more than one peak which are not symmetrical about an axis, the light emitting device optical axis is the angular weighted average of the luminous intensity output. For non-planar output surfaces, the light emitting device optical axis is evaluated in two orthogonal output planes and may be a constant direction in a first output plane and at a varying angle in a second output plane orthogonal to the first output plane. For example, light emitting from a cylindrical light emitting surface may have a peak angular luminous intensity (thus light emitting device optical axis) in a light output plane that does not comprise the curved output surface profile and the angle of luminous intensity could be substantially constant about a rotational axis around the cylindrical surface in an output plane comprising the curved surface profile, and thus the peak angular intensity is a range of angles. When the light emitting device has a light emitting device optical axis in a range of angles, the optical axis of the light emitting device comprises the range of angles or an angle chosen within the range. The optical axis of a lens or element is the direction of which there is some degree of rotational symmetry in at least one plane and as used herein corresponds to the mechanical axis. The optical axis of the region, surface, area, or collection of lenses or elements may differ from the optical axis of the lens or element, and as used herein is dependent on the incident light angular and spatial profile, such as in the case of off-axis illumination of a lens or element.

Light Input Coupler

In one embodiment, a light input coupler comprises a plurality of coupling lightguides disposed to receive light emitting from light source and channel the light into a lightguide. In one embodiment, the plurality of coupling lightguides are strips cut from a lightguide film such that they remain un-cut on at least one edge but can be rotated or positioned (or translated) substantially independently from the lightguide to couple light through at least one edge or surface of the strip. In another embodiment, the plurality of coupling lightguides are not cut from the lightguide film and are separately optically coupled to the light source and the lightguide. In one embodiment, the light input coupler comprises at least one light source optically coupled to the coupling lightguides which join together in a light mixing region. In another embodiment, the light input coupler is a collection of strip sections cut from a region film which are arranged in a grouping such that light may enter through the edge of a grouping or arrangement of strips. In another embodiment, the light emitting device comprises a light input coupler comprising a core region of a core material and a cladding region or cladding layer of a cladding material on at least one face or edge of the core material with a refractive index less than the core material. In other embodiment, the light input coupler comprises a plurality of coupling lightguides wherein a portion of light from a light source incident on the face of at least one strip is directed into the lightguide such that it propagates in a waveguide condition. The light input coupler may also comprise at least one selected from the group: a strip folding device, a strip holding element, and an input surface optical element.

Light Source

In one embodiment, a light emitting device comprises at least one light source selected from the group: fluorescent lamp, cylindrical cold-cathode fluorescent lamp, flat fluorescent lamp, light emitting diode, organic light emitting diode, field emissive lamp, gas discharge lamp, neon lamp, filament lamp, incandescent lamp, electroluminescent lamp, radiofluorescent lamp, halogen lamp, incandescent lamp, mercury vapor lamp, sodium vapor lamp, high pressure sodium lamp, metal halide lamp, tungsten lamp, carbon arc lamp, electroluminescent lamp, laser, photonic bandgap based light source, quantum dot based light source, high efficiency plasma light source, and microplasma lamp. The light emitting device may comprise a plurality of light sources arranged in an array, on opposite sides of lightguide, on orthogonal sides of a lightguide, on 3 or more sides of a lightguide, or on 4 sides of a substantially planer lightguide. The array of light sources may be a linear array with discrete LED packages comprises at least one LED die. In another embodiment, a light emitting device comprises a plurality of light sources within one package disposed to emit light toward a light input surface. In one embodiment, the light emitting device comprises 1, 2, 3, 4, 5, 6, 8, 9, 10, or more than 10 light sources.

In one embodiment, a light emitting device comprises at least one broadband light source that emits light in a wavelength spectrum larger than 100 nanometers. In another embodiment, a light emitting device comprises at least one narrowband light source that emits light in a narrow bandwidth less than 100 nanometers. In another embodiment, a light emitting device comprises at least one broadband light source that emits light in a wavelength spectrum larger than 100 nanometers or at least one narrowband light source that emits light in a narrow bandwidth less than 100 nanometers. In one embodiment a light emitting device comprises at least one narrowband light source with a peak wavelength within a range selected from the group: 300 nm-350 nm, 350 nm-400 nm, 400 nm-450 nm, 450 nm-500 nm, 500 nm-550 nm, 550 nm-600 nm, 600 nm-650 nm, 650 nm-700 nm, 700 nm-750 nm, 750 nm-800 nm, and 800 nm-1200 nm The light sources may be chosen to match the spectral qualities of red, green and blue such that collectively when used in a light emitting device used as a display, the color gamut area is at least one selected from the group: 70% NTSC, 80% NTSC, 90% NTSC, 100% NTSC, and 60%, 70%, 80%, 90%, and 95% of the visible CIE u′ v′ color gamut of a standard viewer. In one embodiment, at least one light source is a white LED package comprising a red, green, and blue LED.

In another embodiment, at least two light sources with different colors are disposed to couple light into the lightguide through at least one light input coupler. In another embodiment, a light emitting device comprises at least three light input couplers, at least three light sources with different colors (red, green and blue for example) and at least three lightguides. In another embodiment, a light source further comprises at least one selected from the group: reflective optic, reflector, reflector cup, collimator, primary optic, secondary optic, collimating lens, compound parabolic collimator, lens, reflective region, and input coupling optic. The light source may also comprise an optical path folding optic such as a curved reflector that can enable the light source (and possibly heat-sink) to be oriented along a different edge of the light emitting device. The light source may also comprise a photonic bandgap structure, nano-structure or other three-dimensional arrangement that provides light output with an angular FWHM less than one selected from the group: 120 degrees, 100 degrees, 80 degrees, 60 degrees, 40 degrees, and 20 degrees.

In another embodiment, a light emitting device comprises a light source emitting light in an angular full-width at half maximum intensity of less than one selected from 150 degrees, 120 degrees, 100 degrees, 80 degrees, 70 degrees, 60 degrees, 50 degrees, 40 degrees, 30 degrees, 20 degrees, and 10 degrees. In another embodiment, the light source further comprises a at least one of a primary optic, secondary optic, and photonic bandgap region and the angular full-width at half maximum intensity of the light source is less than one selected from the group: 150 degrees, 120 degrees, 100 degrees, 80 degrees, 70 degrees, 60 degrees, 50 degrees, 40 degrees, 30 degrees, 20 degrees, and 10 degrees.

Wavelength Conversion Material

In another embodiment, the LED is a blue or ultraviolet LED combined with a phosphor. In another embodiment, a light emitting device comprises a light source with a first activating energy and a wavelength conversion material which converts a first portion of the first activating energy into a second wavelength different than the first. In another embodiment, the light emitting device comprises at least one wavelength conversion material selected from the group: a fluorophore, phosphor, a fluorescent dye, an inorganic phosphor, a photonic bandgap material, a quantum dot material, a fluorescent protein, a fusion protein, a fluorophores attached to protein to specific functional groups, or another wavelength conversion material.

In one embodiment, the light source comprises a semiconductor light emitter such as an LED and a wavelength conversion material that converts a portion of the light from the emitter to a shorter or longer wavelength. In another embodiment, at least one selected from the group: light input coupler, cladding region, coupling lightguide, input surface optic, coupling optic, light mixing region, lightguide, light extraction feature or region, and light emitting surface comprises a wavelength conversion material.

LED Array

In one embodiment, the light emitting device comprises a plurality of LEDs or LED packages wherein the plurality of LEDs or LED packages comprises an array of LEDs. The array components (LEDs or electrical components) may be physically (and/or electrically) coupled to a single circuit board or they may be coupled to a plurality of circuit boards that may or may not be directly physically coupled (i.e. such as not on the same circuit board). In one embodiment, the array of LEDs is an array comprising at least red, green, blue, and white LEDs. In this embodiment, the variation in the white point due to manufacturing or component variations can be reduced. In another embodiment, the LED array comprises at least one white LED and one red LED. In this embodiment, the CRI, or Color Rendering Index, may be higher. In one embodiment, the CRI of at least one of a light emitting region, the light emitting surface, light fixture, light emitting device, display driven in a white mode comprising the light emitting device, or sign is greater than one selected from the group: 70, 75, 80, 85, 90, 95, and 99. In another embodiment, the NIST Color Quality Scale (CQS) of at least one of a light emitting region, the light emitting surface, light fixture, light emitting device, display driven in a white mode comprising the light emitting device, or sign is greater than one selected from the group: 70, 75, 80, 85, 90, 95, and 99. In another embodiment, a display comprising the light emitting device has a color gamut greater than 70%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 120%, and 130% that of the NTSC standard. In another embodiment, the LED array comprises white, green, and red LEDs. In another embodiment, the LED array comprise at least one green and blue LED and two types of red LEDs with one type having a lower luminous efficacy or a lower wavelength than the other type of red LED. Examples of white LEDs include, without limitation, phosphor converted blue LEDs and phosphor converted UV LEDs.

In another embodiment, the input array of LEDs can be arranged to compensate for uneven absorption of light through longer vs. shorter lightguides. In another embodiment, the absorption is compensated for by directing more light into the light input coupler corresponding to the longer coupling lightguides or longer lightguides. In another embodiment, light within a first wavelength band is absorbed within the lightguide more than light within a second wavelength band and the radiant light flux coupled into the light input coupler within the first wavelength band divided by the radiant light flux within the second wavelength band input is greater than the radiant light flux emitted from at least one of the lightguide, light emitting surface of the light emitting device, lightguide region corresponding to light illuminating the waveguide from the two wavelength bands, within the first wavelength band divided by the radiant light flux emitted within the second wavelength band.

Light Input Coupler Input Surface

In one embodiment, the light input coupler comprises a collection of coupling lightguides with a plurality of edges forming a light coupler input surface. In another embodiment, an optical element is disposed between the light source and at least one coupling lightguide wherein the optical element receives light from the light source through a light coupler input surface. In some embodiments, the input surface is substantially polished, flat, or optically smooth such that light does not scatter forwards or backwards from pits, protrusions or other rough surface features. In some embodiments, an optical element is disposed to between the light source and at least one coupling lightguide to provide light redirection as an input surface (when optically coupled to at least one coupling lightguide) or as an optical element separate or optically coupled to at least one coupling lightguide such that more light is redirected into the lightguide at angles greater than the critical angle within the lightguide than would be the case without the optical element or with a flat input surface. In another embodiment, the input surface is curved to refract light more light received from the light source into angles within the lightguide greater than the critical angle within the lightguide than would occur with a flat input surface. In another embodiment, the optical element comprises radial or linear Fresnel lens features which refract incident light. In another embodiment, the optical element comprises a refractive-TIR hybrid Fresnel lens (such as one having a low F/# of less than 1.5). In a further embodiment, the optical element is a reflective and refractive optical element. In one embodiment, the light input surface may be formed by machine, cutting, polishing, forming, molding, or otherwise removing or adding material to the lightguide couplers to create a smooth, curved, rounded, concave, convex, rigged, grooved, micro-structured, nano-structured, or predetermined surface shape. In another embodiment, the light input coupler comprises an optical element designed to collect light from the light source and increase the uniformity. Such optical elements can include fly's eye lenses, microlens arrays, integral lenses, lenticular lenses holographic or other diffusing elements with micro-scale features or nano-scale features independent of how they were formed. In another embodiment, the light input coupler is optically coupled to at least one lightguide and at least one light source. In another embodiment, the optical element is at least one selected from the group: diffractive element, holographic element, lenticular element, lens, planar window, refractive element, reflective element, waveguide coupling element, anti-reflection coated element, planar element, and formed portion or region of at least one selected from the group: coupling lightguide, optical adhesive, UV cured adhesive, and pressure sensitive adhesive. The light coupler or an element therein may be comprised of at least one light transmitting material

When light propagating in air is incident to a planar light input surface of a light transmitting material with a refractive index higher than 1.3 at high angles from the normal to the interface, for example, much of the light is reflected from the air-input surface interface. One method of reducing the loss of light due to reflection is to optically couple the input surface of the light input coupler to the light source. Another method to reduce this loss is to use a collimation optic or optic that directs some of the light output from the light source into angles closer to the optical axis of the light source. The collimating optic, or optical element, may be optically coupled to the light source, the coupling lightguides, an adhesive, or other optical element such that it directs more light into the coupling lightguides into a total internal reflection condition within the coupling lightguides. In another embodiment, the light input surface comprises a recessed cavity or concave region such that the percentage of light from a light source disposed adjacent to the cavity or concave region that is reflected from the input surface is less than one selected from the group: 40%, 30%, 20%, 10%, 5%, 3%, and 2%.

In another embodiment, the total input area ratio, defined as the total area of the input surface of all of the light input couplers of the light emitting device receiving more than 5% of the total light flux from any light source divided by the total light emitting surface areas of the light sources is greater than one selected from the group: 0.9, 1, 1.5, 2, 4, and 5. In another embodiment, the individual input area ratio, defined as the area of the input surface of a light input coupler of the light emitting device receiving more than 5% of the total light flux received from a light source divided by the light emitting surface area of the light source is greater than one selected from the group: 0.9, 1, 1.5, 2, 4, and 5. The individual input area ratios of a light emitting device may vary for different input couplers and the individual input area ratio for a particular input coupler may be greater or less than the total input area ratio.

Stacked Strips or Segments of Film Forming a Light Input Coupler

In one embodiment, the light input coupler is region of a film that comprises the lightguide and the light input coupler which comprises strip sections of the film which form coupling lightguides that are grouped together to form a light coupler input surface. The coupling lightguides may be grouped together such the edges opposite the lightguide region are brought together to form an input surface comprising of their thin edges. A planar input surface for a light input coupler can provide beneficial refraction to redirect a portion of the input light from the surface into angles such that it propagates at angles greater than the critical angle for the lightguide. In another embodiment, a substantially planar light transmitting element is optically coupled to the grouped edges of coupling lightguides. One or more of the edges of the coupling lightguides may be polished, melted, adhered with an optical adhesive, solvent welded, or otherwise optically coupled along a region of the edge surface such that the surface is substantially polished, smooth, flat, or substantially planarized. This polishing can aide to reduce light scattering, reflecting, or refraction into angles less than the critical angle within the coupling lightguides or backwards toward the light source. The light input surface may comprise a surface of the optical element, the surface of an adhesive, the surface of more than one optical element, the surface of the edge of one or more coupling lightguides, or a combination of one or more of the aforementioned surfaces. The light input coupler may also comprise an optical element that has an opening or window wherein a portion of light from a light source may directly pass into the coupling lightguides without passing through the optical element. The light input coupler or an element or region therein may also comprise a cladding material or region.

In another embodiment, the cladding layer is formed in a material wherein under at least one selected from the group: heat, pressure, solvent, and electromagnetic radiation, a portion of the cladding layer may be removed. In another embodiment, a pressure sensitive adhesives functions as a cladding layer and the coupling lightguides are folded such that the pressure sensitive adhesive or component on one or both sides of the coupling lightguides holds the coupling lightguides together and at least 10% of the thickness of the pressure sensitive adhesive is removed from the light input surface by applying heat and pressure.

Guide Device for Coupling the Light Source to the Light Input Surface of the Light Input Coupler

The light input coupler may also comprise a guide that comprises a mechanical, electrical, manual, guided, or other system or component to facility the alignment of the light source in relation to the light input surface. The guide device may comprise an opening or window and may physically or optically couple together one or more selected from the group: light source (or component physically attached to a light source), a light input coupler, coupling lightguide, housing, and electrical, thermal, or mechanical element of the light emitting device. In one embodiment of this device an optical element comprises one or more guides disposed to physically couple or align the light source (such as an LED strip) to the optical element or coupling lightguides. In another embodiment, the optical element comprises one or more guide regions disposed to physically couple or align the optical element to the light input surface of the input coupler. The guide may comprise a groove and ridge, hole and pin, male and corresponding female component, or a fastener.

Coupling Lightguide

In one embodiment, the coupling lightguide is a region wherein light within the region can propagate in a waveguide condition and a portion of the light input into a surface or region of the coupling lightguides passes through the coupling lightguide toward a lightguide or light mixing region. The coupling lightguide, in some embodiments, may serve to geometrically transform a portion of the flux from a light source from a first shaped area to a second shaped area different from the first. In an example of this embodiment, the light input surface of the light input coupler formed from the edges of folded strips (coupling lightguides) of a planar film has a the dimensions of a rectangle that is 3 millimeters by 2.7 millimeters and the light input coupler couples light into a planar section of a film in the light mixing region with a cross-sectional dimensions of 40.5 millimeters by 0.2 millimeters. In one embodiment, the input area of the light input coupler is substantially the same as the cross-sectional area of the light mixing region or lightguide disposed to receive light from one or more coupling lightguides.

In another embodiment, a coupling lightguide is disposed to receive light from at least one input surface with a first input surface longest dimension and transmit the light to a lightguide with a light emitting surface with a light emitting surface longest dimension larger than the first input surface largest dimension. In another embodiment, the coupling lightguide is a plurality of lightguides disposed to collect light from at least one light source through edges or surfaces of the coupling lightguides and direct the light into the surface, edge, or region of a lightguide comprising a light emitting surface. In one embodiment, the coupling lightguides provide light channels whereby light flux entering the coupling lightguides in a first cross sectional area can be redistributed into a second cross sectional area different from the first cross sectional area at the light output region of the light input coupler. The light exiting the light input coupler or light mixing region may then propagate to a lightguide or lightguide region which may be a separate region of the same element (such as a separate region of the same film). In one embodiment, a light emitting device comprises a light source and a film processed to form a lightguide region with light extraction features, a light mixing region wherein light from a plurality of sources, light input couplers, or coupling lightguides mixes before entering into the lightguide region. The coupling lightguides, light mixing region, and light extraction features may all be formed from, on, or within the same film and they may remain interconnected to each other through one or more regions.

In one embodiment, at least one coupling lightguide is disposed to receive light from a plurality of light sources of at least two different colors, wherein the light received by the coupling lightguide is pre-mixed angularly, spatially, or both by reflecting through the coupling lightguide and the 9-spot sampled spatial color non-uniformity, Δu′v′, of the light emitting surface of the light emitting device measured on the 1976 u′, v′ Uniform Chromaticity Scale as described in VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001 (Appendix 201, page 249) is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004 when measured using a spectrometer based spot color meter.

Coupling Lightguide Folds and Bends

In one embodiment, light emitting device comprises a light mixing region disposed between a lightguide and strips or segments cut to form coupling lightguides, whereby a collection of edges of the strips or segments are brought together to form a light input surface of the light input coupler disposed to receive light from a light source. In one embodiment, the light input coupler comprises a coupling lightguide wherein the coupling lightguide comprises at least one fold or bend in one plane such that at least one edge overlaps another edge. In another embodiment, the coupling lightguide comprises a plurality of folds or bends wherein edges of the coupling lightguide can be abutted together in region such that the region forms a light input surface of the light input coupler of the light emitting device.

In one embodiment, a light emitting device comprises a light input coupler comprising at least one coupling lightguide that is bent or folded such that light propagating in a first direction within the lightguide before the bend or fold is propagating in a second direction different that the first within the lightguide after the bend or fold.

In one embodiment, at least one coupling lightguide comprises a strip or segment that is bent or folded to radius of curvature of less than 75 times the thickness of the strip or segment. In another embodiment, at least one coupling lightguide comprises a strip or segment that is bended or folded to radius of curvature greater than 10 times the times the thickness of the strip or segment. In another embodiment, at least one coupling lightguide is bent or folded such that longest dimension in a cross-section through the light emitting device or coupling lightguide in at least one plane is less than without the fold or bend. Segments or strips may be bent or folded in more than one direction or region and the directions of folding or bending may be different between strips or segments.

Collimation of Light Entering the Coupling Lightguides

In one embodiment, at least one selected from the group: light source, light source primary optic, light source secondary optic, light input surface, optical element disposed between the light source and at least one selected from the group: coupling lightguide, shape of the coupling lightguide, shape of the mixing region, shape of the light input coupler, and shape of an element or region of the light input coupler provides light that within the coupling lightguide with an angular full-width of half maximum intensity chosen from the group: less than 80 degrees, less than 70 degrees, less than 60 degrees, less than 50 degrees, less than 40 degrees, less than 30 degrees, less than 20 degrees, less than 10 degrees, between 10 degrees and 30 degrees, between 30 degrees and 50 degrees, between 10 degrees and 60 degrees and between 30 degrees and 80 degrees. In some embodiments, light which is highly collimated (FWHM of about 10 degrees or less) does not mix spatially within a lightguide region with light extracting features such that there may be dark bands or regions of non-uniformity. In this embodiment, the light, however, will be efficiently coupled around curves and bends in the lightguide relative to less collimated light and in some embodiments, the high degree of collimation enables small radii of curvature and thus a smaller volume for the fold or bend in a light input coupler and resulting light emitting device. In another embodiment, a significant portion of light from a light source with a low degree of collimation (FWHM of about 120 degrees) within the coupling lightguides will be reflected into angles such that it exits the coupling lightguides in regions near bends or folds with small radii of curvature. In this embodiment, the spatial light mixing (providing uniform color or luminance) of the light from the coupling lightguides in the lightguide in areas of the light extracting regions is high and the light extracted from lightguide will appear to have a more uniform angular or spatial color or luminance uniformity.

Each light source may be oriented at a different angle. For example, two light sources along one edge of a film with a strip-type light input coupler can be oriented directly toward each other (the optical axes are 180 degrees apart). In another example, the light sources can be disposed in the center of an edge of a film and oriented away from each other (the optical axes are also 180 degrees apart).

The segments or strips may be once folded, for example, with the strips oriented and abutting each other along one side of a film such that the light source optical axis is in a direction substantially parallel with the film plane or lightguide plane. The strips or segments may also be folded twice, for example, such that the light source optical axis is substantially normal to the film plane or normal to the waveguide.

In one embodiment, the fold or bend in the coupling lightguide, region or segment of the coupling lightguide or the light input coupler has a crease or radial center of the bend in a direction that is at a bend angle relative to the light source optical axis. In another embodiment, the bend angle is one selected from the group: 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees, 0-90 degrees, 90-180 degrees, and 0-180 degrees.

The bend or fold may also be of the single directional bend (such as vertical type, horizontal type, 45 degree type or other single angle) or the bend or fold or be multi-directional such as the twisted type wherein the strip or segment is torsional. In one embodiment, the strip, segment or region of the coupling lightguide is simultaneously bent in two directions such that the strip or segment is twisted.

In another embodiment, the light input coupler comprises at least one light source disposed to input light into the edges of strips cut into a film wherein the strips are twisted and aligned with their edges forming an input surface and the light source output surface area is substantially parallel with the edge of the coupling lightguide, lightguide, lightguide region, or light input surface or the optical axis of the light source is substantially perpendicular to the edge of the coupling lightguide, lightguide, lightguide region, or light input surface. In another embodiment, multiple light sources are disposed to couple light into a light input coupler comprising strips cut into a film such that at least one light source has an optical axis substantially parallel to the lightguide edge, coupling lightguide lateral edge or the nearest edge of the lightguide region. In another embodiment, two groupings of coupling lightguides are folded separately toward each other such that the separation between the ends of the strips is substantially the thickness of the central strip between the two groupings and two or more light sources are disposed to direct light in substantially opposite directions into the strips. In one embodiment, two groupings of coupling lightguides are folded separately toward each other such and then both folded in a direction away from the film such that the edges of the coupling lightguides are brought together to form a single light input surface disposed to receive light from at least one light source. In this embodiment, the optical axis of the light source may be substantially normal to the substantially planar film-based lightguide.

In one embodiment, two opposing stacks of coupling lightguides from the same film are folded and recombined at some point away from the end of the coupling apparatus. This can be accomplished by splitting the film into one or more sets of two bundles, which are folded towards each other. In this embodiment, the bundles can be folded at an additional tight radius and recombined into a single stack. The stack input can further be polished to be a flat single input surface or optically coupled to a flat window and disposed to receive light from a light source.

In one embodiment, the combination of the two film stacks is configured to reduce the overall volume. In one embodiment, the film is bent or folded to a radius of curvature greater than 10× the film thickness order to retain sufficient total internal reflection for a first portion of the light propagating within the film.

In another embodiment, the light input coupler comprises at least one coupling lightguide wherein the coupling lightguide comprises an arcuate reflective edge and is folded multiple times in a fold direction substantially parallel to the lightguide edge or nearest edge of the lightguide region wherein multiple folds are used to bring sections of an edge together to form a light input surface with a smaller dimension. In another embodiment, the light coupling lightguide, the strips, or segments have collimating sections cut from the coupling lightguide which directs light substantially more parallel to the optical axis of the light source. In one embodiment, the collimating sections of the coupling lightguide, strips or segments direct light substantially more parallel to the optical axis of the light source in at least one plane substantially parallel to the lightguide or lightguide region.

In a further embodiment, a light input coupler comprises at least one coupling lightguide with an arc, segmented arc, or other light redirect edge cut into a film and the light input coupler comprises a region of the film rolled up to form a spiral or concentric-circle-like light input edge disposed to receive light from a light source.

Width of Coupling Lightguides

In one embodiment, the dimensions of the coupling lightguides are substantially equal in width and thickness to each other such that the input surface areas for each edge surface are substantially the same.

In another embodiment, at least one selected from the group: coupling lightguide width, largest width of a coupling waveguide, average width of the coupling lightguides, and the width of each coupling lightguides is one selected from the group: substantially 0.5 mm-1 mm, 1 mm-2 mm, 2 mm-3 mm, 3 mm-4 mm, 5 mm-6 mm, 0.5 mm-2 mm, 0.5 mm-25 mm, 0.5 mm⁻¹⁰ mm, 10-37 mm, and 0.5 mm-5 mm In one embodiment, at least one selected from the group: the coupling lightguide width, the largest width of a coupling waveguide, the average width of the coupling lightguides, and the width of each coupling lightguides is less than 20 millimeters.

Shaped or Tapered Coupling Lightguides

The width of the coupling lightguides may vary in a predetermined pattern. In one embodiment, the width of the coupling lightguides varies from a large width in a central coupling lightguide to smaller width in lightguides further from the central coupling lightguide as viewed when the light input edges of the coupling lightguides are disposed together to form a light input surface on the light input coupler. In this embodiment, a light source with a substantially circular light output aperture can couple into the coupling lightguides such that the light at higher angles from the optical axis are coupled into a smaller width strip such that the uniformity of the light emitting surface along the edge of the lightguide or lightguide region and parallel to the input edge of the lightguide region disposed to receive the light from the coupling lightguides is greater than one selected from the group: 60%, 70%, 80%, 90% and 95%.

Other shapes of stacked coupling lightguides can be envisioned, such as triangular, square, rectangular, oval, etc. that provide matched input areas to the light emitting surface of the light source. The widths of the coupling lightguides may also be tapered such that they redirect a portion of light received from the light source. The lightguides may be tapered near the light source, in the area along the coupling lightguide between the light source and the lightguide region, near the lightguide region, or some combination thereof.

In some embodiments, one light source will not provide sufficient light flux to enable the desired luminance or light output profile desired for a particular light emitting device. In this example, one may use more than one light input coupler and light source along and edge or side of a lightguide region or light mixing region. In one embodiment, the average width of the coupling lightguides for at least one light input coupler are in a first width range of one selected from the group: 1-3, 1.01-3, 1.01-4, 0.7-1.5, 0.8-1.5, 0.9-1.5, 1-2, 1.1-2, 1.2-2, 1.3-2, 1.4-2, 0.7-2, 0.5-2, and 0.5-3 times the largest width of the light output surface of the light source in the direction of the lightguide coupler width at the light input surface.

Coupling Lightguides Directed into More than One Light Input Surface

In a further embodiment, the coupling lightguides collectively do not couple light into the light mixing region, lightguide, or light mixing region in a contiguous manner. For example, every other coupling lightguide may be cut out from the film based lightguide while still providing strips or coupling lightguides along one or more edges, but not continuously coupling light into the lightguide regions. By using fewer lightguides, the collection of light input edges may be reduced in size. This reduction in size, for example, can be used to combine multiple sets of coupling lightguides optically coupled to different regions of the same lightguide or a different lightguide, better match the light input surface size to the light source size, use a smaller light source, or use a thicker lightguide film with a particular light source where the dimension of the set of contiguous coupling lightguides in the thickness direction would be one selected from the group: 10%, 20%, 40%, 50%, and 100% greater than light emitting surface of the light source in the thickness direction when disposed to couple light into the light input surface.

In a further embodiment, coupling lightguides from a first region of a lightguide have light input edges collected into two or more light input surfaces. For example, the odd number coupling lightguides may be directed to a first white light source and the even number coupling lightguides may be coupled to a red, green, and blue light source. In another embodiment, the coupling lightguides from a first region of a lightguide are coupled to a plurality of white light sources to reduce visibility of color variations from the light source. For example, the even number coupling lightguides may couple light from a white light source with a first color temperature and the odd number coupling lightguides may couple light from a white light source with a second color temperature higher than the first such that the color non-uniformity, Δu′v′, along a direction parallel to an edge of the lightguide region along the light emitting surface is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004.

Similarly, three or more light input surfaces may also be used to couple light from 1, 2, 3 or more light sources. For example, every alternating first, second, and third coupling lightguide from a first region of a lightguide are directed to a first, second, and third light source of the same or different colors.

In a further embodiment, coupling lightguides from a first region of a lightguide have light input edges collected into two or more light input surfaces disposed to couple light into the lightguide for different modes of operation. For example, the first light input surface may be coupled to at least one light source suitable for daylight compatible output and the second light input surface may be coupled to at least one light source for NVIS compatible light output.

The order of the coupling lightguides directed to more than one light input surface do not need to be alternating and may be of any predetermined or random configuration. For example, the coupling lightguides from the top and bottom region of the lightguide may be directed to a different light input surface than the middle region. In a further embodiment, the coupling lightguides from a region of the lightguide are disposed together into a plurality of light input surfaces, each comprising more than one light input edge, arranged in an array, disposed to couple light from a collection of light sources, disposed within the same housing, disposed such that the light input surfaces are disposed adjacent each other, disposed in an order transposed to receive light from a collection of light sources, disposed in a non-contiguous arrangement wherein neighboring light input surfaces do not couple light into neighboring regions of the lightguide, lightguide region, or light mixing region.

In a further embodiment, a plurality of sets of coupling lightguides are arranged to provide a plurality of sets of light input surface along the same side, edge, the back, the front or within the same housing region of the light emitting device wherein the plurality of light input surfaces are disposed to receive light from one or a plurality of LEDs.

Order of Coupling Lightguides

In one embodiment, the coupling lightguides are disposed together at a light input edge forming a light input surface such that the order of the strips in a first direction is the order of the coupling lightguides as they direct light into the lightguide or lightguide region. In another embodiment, the coupling lightguides are interleaved such that the order of the strips in a first direction is not the same as the order of the coupling lightguides as they direct light into the lightguide or lightguide region. In one embodiment, the coupling lightguides are interleaved such that at least one coupling lightguide receiving light from a first light source of a first color is disposed between two coupling lightguides at a region near the lightguide region or light mixing region that receive light from a second light source with a second color different from the color of the first light source. In one embodiment, the color non-uniformity, Δu′v′, along a direction parallel to the edge of the lightguide region along the light emitting surface is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004. In another embodiment, the coupling lightguides are interleaved such that at least one pair of coupling lightguides adjacent to each other at the output region of the light input coupler near the light mixing region, lightguide, or lightguide region, are not adjacent to each other near the input surface of the light input coupler. In one embodiment, the interleaved coupling lightguides are arranged such that the non-uniform angular output profile is made more uniform at the output of the light input coupler by distributing the coupling lightguides such that output from the light input coupler does not spatially replicate the angular non-uniformity of the light source. For example, the strips of a light input coupler could alternate among four different regions of the lightguide region as they are combined at the light input surface so that the middle region would not have very high luminance light emitting surface region that corresponds to the typically high intensity from a light source at 0 degrees or along its optical axis.

The coupling lightguides may direct light from a light source disposed along the top, bottom, or both into one or more sides of a display such that the light is substantially travelling parallel to the bottom and top edges within the lightguide region.

Coupling Lightguides Bonded to the Surface of a Lightguide Region

In one embodiment, the coupling lightguides are not segmented (or cut) regions of the same film which comprises the lightguide or lightguide region. In one embodiment, the coupling lightguides are formed and physically or optically attached to the lightguide, light mixing region, or lightguide region using at least one selected from the group: optical adhesive, bonding method (solvent welding, thermally bonding, ultrasonic welding, laser welding, hot gas welding, freehand welding, speed tip welding, extrusion welding, contact welding, hot plate welding, high frequency welding, injection welding, friction welding, spin welding, welding rod), and adhesive or joining techniques suitable for polymers.

In one embodiment, at least one coupling lightguide is optically coupled to at least one selected from the group: a surface, edge, or interior region, of an input light coupler, light mixing region, lightguide region, and lightguide. In another embodiment, a film comprising parallel linear cuts along the a direction of a film is bonded to a surface of a film in the extrusion process such that the strips are optically coupled to the lightguide film and the cut regions can be cut in the transverse direction to “free” the strips so that they can be brought together to form a light input surface of a light input coupler.

Light Mixing Region

In one embodiment, a light emitting device comprises a light mixing region disposed in an optical path between the light input coupler and the lightguide region. The light mixing region can provide a region for the light output from individual coupling lightguides to mix together and improve at least one of the spatial luminance uniformity, spatial color uniformity, angular color uniformity, angular luminance uniformity, angular luminous intensity uniformity or any combination thereof within a region of the lightguide or of the surface or output of the light emitting region or light emitting device. In one embodiment, the width of the light mixing region is selected from a range from 0.1 mm (for small displays) to more than 3.048 meters (for large billboards). In one embodiment, the light mixing region is the region disposed along an optical path near the end region of the coupling lightguides whereupon light from two or more coupling lightguides may inter-mix and subsequently propagate to a light emitting region of the lightguide. In one embodiment, the light mixing region is formed from the same component or material as at least one of the lightguide, lightguide region, light input coupler, and coupling lightguides. In another embodiment, the light mixing region comprises a material that is different than at least one selected from the group: lightguide, lightguide region, light input coupler, and coupling lightguides. The light mixing region may be a rectangular, square or other shaped region or it may be a peripheral region surrounding all or a portion of the light emitting region or lightguide region.

Cladding Layer

In one embodiment, at least one of the light input coupler, coupling lightguide, light mixing region, lightguide region, and lightguide comprises a cladding layer optically coupled to at least one surface. A cladding region, as used herein, is a layer optically coupled to a surface wherein the cladding layer comprises a material with a refractive index, n_(clad), less than the refractive index of the material, n_(m), of the surface to which it is optically coupled. In one embodiment, n_(m)-n_(clad) is one selected from the group: 0.001-0.005, 0.001-0.01, 0.001-0.1, 0.001-0.2, 0.001-0.3, 0.001-0.4, 0.01-0.1, 0.1-0.5, 0.1-0.3, 0.2-0.5, greater than 0.01, greater than 0.1, greater than 0.2, and greater than 0.3. In one embodiment, the cladding is one selected from the group: methyl based silicone pressure sensitive adhesive, fluoropolymer material (applied with using coating comprising a fluoropolymer substantially dissolved in a solvent), and a fluoropolymer film. The cladding layer may be incorporated to provide a separation layer between the core or core part of a lightguide region and the outer surface to reduce undesirable out-coupling (for example, frustrated totally internally reflected light by touching the film with an oily finger) from the core or core region of a lightguide. Components or objects such as additional films, layers, objects, fingers, dust etc. that come in contact or optical contact directly with a core or core region of a lightguide may couple light out of the lightguide, absorb light or transfer the totally internally reflected light into a new layer. By adding a cladding layer with a lower refractive index than the core, a portion of the light will totally internally reflect at the core-cladding layer interface. Cladding layers may also be used to provide the benefit of at least one of increased rigidity, increased flexural modulus, increased impact resistance, anti-glare properties, provide an intermediate layer for combining with other layers such as in the case of a cladding functioning as a tie layer or a base or substrate for an anti-reflection coating, a substrate for an optical component such as a polarizer, liquid crystal material, increased scratch resistance, provide additional functionality (such as a low tack adhesive to bond the lightguide region to another element, a window “cling type” film such as a highly plasticized PVC). The cladding layer may be an adhesive, such as a low refractive index silicone adhesive which is optically coupled to another element of the device, the lightguide, the lightguide region, the light mixing region, the light input coupler, or a combination of one or more of the aforementioned elements or regions. In one embodiment, a cladding layer is optically coupled to a rear polarizer in a backlit liquid crystal display.

Cladding Location

In one embodiment, the cladding region is optically coupled to at least one selected from the group: lightguide, lightguide region, light mixing region, one surface of the lightguide, two surfaces of the lightguide, light input coupler, coupling lightguides, and an outer surface of the film. In another embodiment, the cladding is disposed in optical contact with the lightguide, lightguide region, or layer or layers optically coupled to the lightguide and the cladding material is not disposed on one or more coupling lightguides. In one embodiment, the coupling lightguides do not comprise a cladding region on either planar side and optical loss at the bends or folds in the coupling lightguides is reduced. In another embodiment, the coupling lightguides do not comprise a cladding region on either planar side and the light input surface input coupling efficiency is increased due to the light input surface area having a higher concentration of lightguide received surface relative to a lightguide with at least one cladding.

In one embodiment, the cladding on at least one surface of the lightguide is applied (such as coated or co-extruded) and the cladding on the coupling lightguides is subsequently removed. In a further embodiment, the cladding applied on the surface of the lightguide (or the lightguide is applied onto the surface of the cladding) such that the regions corresponding to the coupling lightguides do not have a cladding. For example, the cladding material could be extruded or coated onto a lightguide film in a central region wherein the outer sides of the film will comprise coupling lightguides. Similarly, the cladding may be absent on the coupling lightguides in the region disposed in close proximity to one or more light sources or the light input surface.

In one embodiment, two or more core regions of the coupling lightguides do not comprise a cladding region between the core regions in a region of the coupling lightguide disposed within a distance selected from the group: 1 millimeter, 2 millimeters, 4 millimeters, and 8 millimeters from the light input surface edge of the coupling lightguides. In a further embodiment, two or more core regions of the coupling lightguides do not comprise a cladding region between the core regions in a region of the coupling lightguide disposed within a distance selected from the group: 10%, 20%, 50%, 100%, 200%, and 300% of the combined thicknesses of the cores of the coupling lightguides disposed to receive light from the light source from the light input surface edge of the coupling lightguides. In one embodiment, the coupling lightguides in the region proximate the light input surface do not comprise cladding between the core regions (but may contain cladding on the outer surfaces of the collection of coupling lightguides) and the coupling lightguides are optically coupled together with an index-matching adhesive or material or the coupling lightguides are optically bonded, fused, or thermo-mechanically welded together by applying heat and pressure. In a further embodiment, a light source is disposed at a distance to the light input surface of the coupling lightguides less than one selected from the group: 0.5 millimeter, 1 millimeter, 2 millimeters, 4 millimeters, and 6 millimeters and the dimension of the light input surface in the first direction parallel to the thickness direction of the coupling lightguides is greater than one selected from the group: 100%, 110%, 120%, 130%, 150%, 180%, and 200% the dimension of the light emitting surface of the light source in the first direction. In another embodiment, disposing an index-matching material between the core regions of the coupling lightguides or optically coupling or boding the coupling lightguides together in the region proximate the light source optically couples at least one selected from the group: 10%, 20%, 30%, 40%, and 50% more light into the coupling lightguides than would be coupled into the coupling lightguides with the cladding regions extending substantially to the light input edge of the coupling lightguide. In one embodiment, the index-matching adhesive or material has a refractive index difference from the core region less than one selected from the group: 0.1, 0.08, 0.05, and 0.02. In another embodiment, the index-matching adhesive or material has a refractive index greater by less than one selected from the group: 0.1, 0.08, 0.05, and 0.02 the refractive index of the core region. In a further embodiment, a cladding region is disposed between a first set of core regions of coupling lightguides for a second set of coupling lightguides an index-matching region is disposed between the core regions of the coupling lightguides or they are fused together. In a further embodiment, the coupling lightguides disposed to receive light from the geometric center of the light emitting area of the light source within a first angle of the optical axis of the light source have cladding regions disposed in-between the core regions, and the core regions at angles larger than the first angle have index-matching regions disposed between the core regions of the coupling lightguides or they are fused together. In one embodiment, the first angle is selected from the group: 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, and 60 degrees. In the aforementioned embodiments, the cladding region may be a low refractive index material or air.

Cladding Layer Materials

In one embodiment, the cladding layer comprises an adhesive such as a silicone-based adhesive, acrylate-based adhesive, epoxy, radiation curable adhesive, UV curable adhesive, or other light transmitting adhesive. Other low refractive index materials, fluoropolymer materials, polymers and adhesives may be used in some embodiments.

Light Input Couplers Disposed Near More than One Edge of a Lightguide

In one embodiment, a light emitting device comprises a plurality of light input couplers disposed to couple light into a lightguide from at least two input regions disposed near two different edges of a lightguide. In another embodiment, two light input couplers are disposed on opposite sides of a lightguide. In another embodiment, light input couplers are disposed on three or four sides of a film-type lightguide. In a further embodiment, more than one light input coupler, housing, or light input surface is disposed to receive light from a single light source, light source package, array of light sources or light source strip (such as a substantially linear array of LEDs). For example, two housing for two light input couplers disposed to couple light to two different regions of a lightguide are disposed to receive light from a substantially linear array of LEDs. In another embodiment a first input surface comprising a first collection of coupling lightguides optically coupled to a first region of a lightguide and a second input surface comprising a second collection of coupling lightguides optically coupled to a second region of a lightguide different than the first region are disposed to receive light from one selected from the group: the same light source, a plurality of light sources, light sources in a package, an array or collection of light sources, a linear array of light sources, one or more LEDs, an LED package, a linear array of LEDs, and LEDs of multiple colors.

Curved or Flexible Housing

In another embodiment, the housing comprises at least one curved surface. A curved surface can permit non-linear shapes or devices or facilitate incorporating non-planer or bent lightguides or coupling lightguides. In one embodiment, a light emitting device comprises a housing with at least one curved surface wherein the housing comprises curved or bent coupling lightguides.

Housing Including a Thermal Transfer Element

In one embodiment, the housing comprises a thermal transfer element disposed to transfer heat from a component within the housing to an outer surface of the housing. In another embodiment, the thermal transfer element is one selected from the group: heat sink, metallic or ceramic element, fan, heat pipe, synthetic jet, air jet producing actuator, active cooling element, passive cooling element, rear portion of a metal core or other conductive circuit board, thermally conductive adhesive, and other component known to thermally conduct heat. In one embodiment, the thermal transfer element has a thermal conductivity (W/(m˜K)) greater than one selected from the group: 0.2, 0.5, 0.7, 1, 3, 5, 50, 100, 120, 180, 237, 300, and 400.

Lightguide Configuration and Properties

The use of plastic film with thickness less than 0.5 mm for edge lit lightguides can hold many advantages over using plastic plate or sheets, such as a lower cost. A flexible film may be able to be shaped to surfaces, be folded up for storage, change shape as needed, or wave in the air.

Thickness of the Film or Lightguide

In one embodiment, the thickness of the film, lightguide or lightguide region is within a range of 0.005 mm to 0.5 mm. In another embodiment, the thickness of the film or lightguide is within a range of 0.025 millimeters to 0.5 millimeters. In a further embodiment, the thickness of the film, lightguide or lightguide region is within a range of 0.050 millimeters to 0.175 millimeters. In one embodiment, the thickness of the film, lightguide or lightguide region is less than 0.2 millimeters or less than 0.5 millimeters.

Optical Properties of the Lightguide or Light Transmitting Material

With regards to the optical properties of lightguides or light transmitting materials for embodiments, the optical properties specified herein may be general properties of the lightguide, the core, the cladding, or a combination thereof or they may correspond to a specific region (such as a light emitting region, light mixing region, or light extracting region), surface (light input surface, diffuse surface, flat surface), and direction (such as measured normal to the surface or measured in the direction of light travel through the lightguide).

In one embodiment, the use of a thin film for the lightguide permits the reduction in size of light extraction features because more waveguide modes will reach the light extraction feature when the thickness of the film is reduced. In a thin lightguide, the overlap of modes is increased when the thickness of the waveguide is reduced.

In one embodiment, the light transmitting material used in at least one selected from the group: the coupling lightguide, lightguide, lightguide region, optical element, optical film, core layer, cladding layer, and optical adhesive has an optical absorption (dB/km) less than one selected from the group: 50, 100, 200, 300, 400, and 500 dB/km for a wavelength range of interest. The optical absorption value may be for all of the wavelengths throughout the range of interest or an average value throughout the wavelengths of interest. The wavelength range of interest for high transmission through the light transmitting material may cover the light source output spectrum, the light emitting device output spectrum, optical functionality requirements (IR transmission for cameras, motion detectors, etc., for example), or some combination thereof. The wavelength range of interest may be a wavelength range selected from the group: 400 nm-700 nm, 300 nm-800 nm, 300 nm-1200 nm, 300 nm-350 nm, 300-450 nm, 350 nm-400 nm, 400 nm-450 nm, 450 nm-490 nm, 490 nm-560 nm, 500 nm-550 nm, 550 nm-600 nm, 600 nm-650 nm, 635 nm-700 nm, 650 nm-700 nm, 700 nm-750 nm, 750 nm-800 nm, and 800 nm-1200 nm.

In another embodiment, the lightguide is the substrate for a display technology. Various high performance films are known in the display industry as having sufficient mechanical and optical properties. These include, but are not limited to polycarbonate, PET, PMMA, PEN, COC, PSU, PFA, FEP, and films made from blends and multilayer components. In one embodiment, the light extraction feature is formed in a lightguide region of a film before or after the film is utilized as a substrate for the production or use as a substrate for a display such as an OLED display, MEMs based display, polymer film based display, bi-stable display, electrophoretic display, electrochromic display, electro-optical display, passive matrix display, or other display that can be produced using polymer substrates.

Refractive Index of the Light Transmitting Material

In one embodiment, the core material of the lightguide has a high refractive index and the cladding material has a low refractive index. In one embodiment, the core is formed from a material with a refractive index (n_(D)) greater than one selected from the group: 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0. In another embodiment, the refractive index (n_(D)) of the cladding material is less than one selected from the group: 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, and 2.5.

The core or the cladding or other light transmitting material used within an embodiment may be a thermoplastic, thermoset, rubber, polymer, silicone or other light transmitting material. Optical products can be prepared from high index of refraction materials, including monomers such as high index of refraction (meth)acrylate monomers, halogenated monomers, and other such high index of refraction monomers as are known in the art. Low refractive index materials include sol gels, fluoropolymers, fluorinated sol-gels, PMP, and other materials such fluoropolyether urethanes, and other low refractive index materials known in the industry. Materials such a nanoparticles (Titanium dioxide, and other oxides for example), blends, alloys, doping, sol gel, and other techniques may be used to increase or decrease the refractive index of a material.

Edges of the Lightguide

In one embodiment, the edges of the lightguide or lightguide region are coated, bonded to or disposed adjacent to a specularly reflecting material, partially diffusely reflecting material, or diffuse reflecting material. In another embodiment, the edges of the lightguide are tapered, angled serrated, or otherwise cut or formed such that light from a light source propagating within the coupling lightguide reflects from the edge such that it is directed into an angle closer to the optical axis of the light source, toward a folded region, toward a bent region, toward a lightguide, toward a lightguide region, or toward the optical axis of the light emitting device. In a further embodiment, two or more light sources are disposed to each couple light into two or more coupling lightguides comprising light re-directing regions for each of the two or more light sources that comprise first and second reflective surfaces which direct a portion of light from the light source into an angle closer to the optical axis of the light source, toward a folded or bent region, toward a lightguide region, toward a lightguide region, or toward the optical axis of the light emitting device.

Surfaces of the Lightguide

In one embodiment, at least one surface of the lightguide or lightguide region is coated, bonded to or disposed adjacent to a specularly reflecting material, partially diffusely reflecting material, or diffuse reflecting material. In one embodiment, at least on lightguide surface is coated with a specularly reflecting ink comprising nano-sized or micron-sized particles or flakes which reflect the light substantially specularly.

Shape of the Lightguide

In one embodiment, at least a portion of the lightguide shape or lightguide surface is at least one selected from the group: substantially planar, curved, cylindrical, a formed shape from a substantially planar film, spherical, partially spherical, angled, twisted, rounded, have a quadric surface, spheroid, cuboid, parallelepiped, triangular prism, rectangular prism, ellipsoid, ovoid, cone pyramid, tapered triangular prism, and other known geometrical solids or shapes. In one embodiment, the lightguide is a film which has been formed into a shape by thermoforming or other forming technique. In another embodiment, the film or region of the film is tapered in at least one direction. In a further embodiment, a light emitting device comprises a plurality of lightguides and a plurality of light sources physically couple or arranged together (such as tiled in a 1×2 array for example). In another embodiment, the lightguide region of the film comprises or is substantially in the shape of one selected from the group: rectangular, square, circle, doughnut shaped (elliptical with a hole in the inner region), elliptical, linear strip, and tube (with a circular, rectangular, polygonal, or other shaped cross-section).

In one embodiment, a light emitting device comprises a lightguide formed from a film into a hollow cylindrical tube comprises coupling lightguide strips branching from the film on a short edge toward the inner portion of the cylinder. In another embodiment, a light emitting device comprises a film lightguide with coupling lightguides cut into the film so that they remain coupled to the lightguide region and the central strip is not optically coupled to the lightguide and provides a spine with increased In another embodiment, a light emitting device comprises light emitting lightguides wherein the separation between the lightguides in at least one direction along the light emitting surface is less than one selected from the group: 10 mm, 5 mm, 3 mm, 2 mm, 1 mm, and 0.5 mm.

In another embodiment, the lightguide comprises single fold or bend near an edge of the lightguide such that the lightguide folds under or over itself. In this embodiment, light which would ordinarily be lost at the edge of a lightguide may be further extracted from the lightguide after the fold or bend to increase the optical efficiency of the lightguide or device. In another embodiment, the light extraction features on the lightguide disposed in the optical path of the light within the lightguide after the fold or bend provide light extraction features that increase at least one selected from the group: the luminance, luminance uniformity, color uniformity, optical efficiency, and image or logo clarity or resolution.

Lightguide Material

In one embodiment, a light emitting device comprises a lightguide or lightguide region formed from at least one light transmitting material. In one embodiment, the lightguide is a film comprising at least one core region and at least one cladding region, each comprising at least one light transmitting material.

The light transmitting material used within an embodiment may be a thermoplastic, thermoset, rubber, polymer, high transmission silicone, glass, composite, alloy, blend, silicone, other light transmitting material, or a combination thereof

Light Extraction Method

In one embodiment, at least one of the lightguide, lightguide region, or light emitting region comprises at least one light extraction feature or region. In one embodiment, the light extraction region may be a raised or recessed surface pattern or a volumetric region. Raised and recessed surface patterns include scattering material, raised lenses, scattering surfaces, pits, grooves, surface modulations, microlenses, lenses, diffractive surface features, holographic surface features, wavelength conversion materials, holes, edges of layers (such as regions where the cladding is removed from covering the core layer), pyramid shapes, prism shapes, and other geometrical shapes with flat surfaces, curved surfaces, random surfaces, quasi-random surfaces, and combinations thereof. The volumetric scattering regions within the light extraction region may comprise dispersed phase domains, voids, absence of other materials or regions (gaps, holes), air gaps, boundaries between layers and regions, and other refractive index discontinuities within the volume of the material different that co-planar layers with parallel interfacial surfaces.

In one embodiment, the lightguide or lightguide region comprises light extraction features in a plurality of regions. In one embodiment, the lightguide or lightguide region comprises light extraction features on or within at least one selected from the group: one outer surface, two outer surfaces, two outer and opposite surfaces, an outer surface and at least one region disposed between the two outer surfaces, within two different volumetric regions substantially within two different volumetric planes parallel to at least one outer surface or light emitting surface or plane, and within a plurality of volumetric planes. In another embodiment, a light emitting device comprises a light emitting region on the lightguide region of a lightguide comprising more than one region of light extraction features.

In one embodiment, at least one light extraction feature is an array, pattern or arrangement of a wavelength conversion material, specularly reflecting, diffusely reflecting, or a combination thereof material. For example, the light extraction feature may be a substantially specularly reflecting ink disposed at an angle (such as coated onto a groove) or it may be a substantially diffusely reflective ink such as an ink comprising titanium dioxide particles within a methacrylate-based binder (white paint).

The pattern or arrangement of light extraction features may vary in size, shape, pitch, location, height, width, depth, shape, orientation, in the x, y, or z directions.

Multiple Lightguides

In one embodiment, a light emitting device comprises more than one lightguide to provide at least one selected from the group: color sequential display, localized dimming backlight, red, green, and blue lightguides, animation effects, multiple messages of different colors, NVIS and daylight mode backlight (one lightguide for NVIS, one lightguide for daylight for example), tiled lightguides or backlights, and large area light emitting devices comprised of smaller light emitting devices. In another embodiment, a light emitting device comprises a plurality of lightguides optically coupled to each other. In another embodiment, at least one lightguide or a component thereof comprises a region with anti-blocking features such that the lightguides do not substantially couple light directly into each other due to touching. In some embodiments, the need for a cladding can be reduced or alleviated by using anti-blocking materials to maintain separation (and air gap) over regions of the lightguide surfaces. In another embodiment, the light emitting device comprises a first and second light emitting region disposed to receive light from a first and second group of coupling lightguides, respectively, wherein the bends or folds in the first group of coupling lightguides are at angle selected from the group: 10 to 30 degrees, 25 degrees to 65 degrees, 70 to 110 degrees, 115 degrees to 155 degrees, 160 degrees to 180 degrees, and 5 to 180 degrees from the bends or folds in the second group of coupling lightguides.

In another embodiment, a film based lightguide has two separate light emitting regions with a first and second group of coupling lightguides disposed to couple light into the first light emitting region and second light emitting region, respectively, wherein the first and second groups of coupling lightguides fold or bend to create a single light input coupler disposed to couple light from a single source or source package into both light emitting regions.

In another embodiment, two film based lightguides are disposed above one another in at least one selected from the group: lightguide region, light output region, light input coupler, light input surface, and light input edge such that light from a light source, a package of light sources, an array of light sources, or an arrangement of light sources is directed into more than one film-based lightguide.

In a further embodiment, a plurality of lightguides are disposed substantially parallel to each other proximate a first light emitting region and the lightguides emit light of a first and second color. The colors may be the same or different and provide additive color, additive luminance, white light emitting lightguides, red, green, and blue light emitting lightguides or other colors or combinations of lightguides emitting light near the same, adjacent or other corresponding light emitting regions or light extraction features. In another embodiment, a light emitting device comprises a first lightguide and a second lightguide wherein a region of the second lightguide is disposed beneath first lightguide in a direction parallel to the optical axis of the light emitting device or parallel to the normal to the light emitting surface of the device and at least one coupling lightguide from the first light lightguide is interleaved between at least two coupling lightguides from the second lightguide. In a further embodiment, the coupling lightguides from the first lightguide film are interleaved with the coupling lightguides of the second lightguide region.

Lightguide Folding Around Components

In one embodiment, at least one selected from the group: lightguide, lightguide region, light mixing region, plurality of lightguides, coupling lightguides, and light input coupler bends or folds such that components of the light emitting device are hidden from view, located behind another component or the light emitting region, or are partially or fully enclosed. These components around which they may bend or fold include components of the light emitting device such as light source, electronics, driver, circuit board, thermal transfer element, spatial light modulator, housing, holder, or other components are disposed behind the folded or bent lightguide or other region or component. In one embodiment, a frontlight for a reflective display comprises a lightguide, coupling lightguides and a light source wherein the light source is disposed substantially behind the display.

Registration Holes

In one embodiment, at least one selected from the group: lightguide, lightguide region, light mixing region, light input coupler, housing, holding device, and plurality of coupling lightguides comprises at least one hole, opening, or aperture suitable for registration with another component of the device that contains at least one pin or object which may pass through the at least one hole.

Other Components

In one embodiment, the light emitting device comprises at least one selected from the group: power supply, batteries (which may be aligned for a low profile or low volume device), thermal transfer element (such as a heat sink, heat pipe, or stamped sheet metal heat sink), frame, housing, heat sink extruded and aligned such that it extends parallel to at least one side of the lightguide, multiple folding or holding modules along a thermal transfer element or heat sink, thermal transfer element exposed to thermally couple heat to a surface external to the light emitting device, and solar cell capable of providing power, communication electronics (such as needed to control light sources, color output, input information, remote communication, Wi-Fi control, Bluetooth control, wireless internet control, etc.), a magnet for temporarily affixing the light emitting device to a ferrous or suitable metallic surface, motion sensor, proximity sensor, forward and backwards oriented motion sensors, optical feedback sensor (including photodiodes or LEDs employed in reverse as detectors), controlling mechanisms such as switches, dials, keypads (for functions such as on/off, brightness, color, color temp, presets (for color, brightness, color temp, etc.), wireless control), externally triggered switches (door closing switch for example), synchronized switches, and light blocking elements to block external light from reaching the lightguide or lightguide region or to block light emitted from a region of the light emitting device from being seen by a viewer.

In one embodiment, a light emitting device comprises a first set of light sources comprising a first and second light source disposed to couple light into a first and second light input coupler, respectively, and further comprising a second set of light sources comprising a third and fourth light source disposed to couple light into a first and second light input coupler, respectively. The first set of light sources are thermally coupled to each other and the second set of light sources are thermally coupled to each other by means including one or more of the following: a metal core printed circuit board, an aluminum component, a copper component, a metal alloy component, a thermal transfer element, or one or more other thermally conducting elements. In a further embodiment, the first and second set of light sources are substantially thermally isolated by separating the light sources (or substrates for the light sources such as a PCB) in the region proximate the light sources by an air gap or substantially thermally insulating material such as polymer substantially free of metallic, ceramic, or thermally conducting components. In another embodiment, the first and third light sources are disposed closer to each other than the first and second light sources and more heat from the first light source reaches the second light source than reaches the third light source when only the first light source is emitting light. More than two light sources disposed to couple light into more than two coupling lightguides may be thermally coupled together by a thermal transfer element and may be separated from a second set of more than two light sources by an air gap or thermally insulating material.

In another embodiment, a light emitting device comprises a film lightguide that emits light and also detects light changes within the lightguide and provides touch screen functionality

Thermal Transfer Element Coupled to Coupling Lightguide

In another embodiment, a thermal transfer element is thermally coupled to a cladding region, lightguide region, lightguide, coupling lightguide, stack or arrangement of coupling lightguides, combination of folded regions in a coupling lightguide, input coupler, window or housing component of the light input coupler, or housing.

Other Optical Films

In another embodiment, the light emitting device further comprises a light redirecting optical film, element, or region that redirects light incident at a first range of angles, wavelength range, and polarization range into a second range of angles different than the first

Light Redirecting Element Disposed to Redirect Light from the Lightguide

In one embodiment, a light emitting device comprises a lightguide with light redirecting elements disposed on or within the lightguide and light extraction features disposed in a predetermined relationship relative to one or more light redirecting elements. In another embodiment, a first portion of the light redirecting elements are disposed above a light extraction feature in a direction substantially perpendicular to the light emitting surface, lightguide, or lightguide region.

Backlight or Frontlight

In one embodiment, a light emitting display backlight or frontlight comprises a light source, a light input coupler, and a lightguide. In one embodiment, the frontlight or backlight illuminates a display or spatial light modulator selected from the group: liquid crystal displays (LCDs), MEMs based display, electrophoretic displays, cholesteric display, time-multiplexed optical shutter display, color sequential display, interferometric modulator display, bistable display, electronic paper display, LED display, TFT display, OLED display, carbon nanotube display, nanocrystal display, head mounted display, head-up display, segmented display, passive matrix display, active matrix display, twisted nematic display, in-plane switching display, advanced fringe field switching display, vertical alignment display, blue phase mode display, zenithal bistable device, reflective LCD, transmissive LCD, electrostatic display, electrowetting display, bistable TN displays, micro-cup electrophoretic displays, grating aligned zenithal display, photonic crystal display, electrofluidic display, and electrochromic displays.

LCD Backlight or Frontlight

In one embodiment, a backlight or frontlight suitable for use with a liquid crystal display panel comprises at least one light source, light input coupler, and lightguide. In one embodiment, the backlight or frontlight comprises a single lightguide wherein the illumination of the liquid crystal panel is white. In another embodiment, the backlight or frontlight comprises a plurality of lightguides disposed to receive light from at least two light sources with two different color spectra such that they emit light of two different colors. In another embodiment, the backlight or frontlight comprises a single lightguide disposed to receive light from at least two light sources with two different color spectra such that they emit light of two different colors. In another embodiment, the backlight or frontlight comprises a single lightguide disposed to receive light from a red, green and blue light source. In one embodiment, the lightguide comprises a plurality of light input couplers wherein the light input couplers emit light into the lightguide with different wavelength spectrums or colors. In another embodiment, light sources emitting light of two different colors or wavelength spectrums are disposed to couple light into a single light input coupler. In this embodiment, more than one light input coupler may be used and the color may be controlled directly by modulating the light sources.

In a further embodiment, the backlight or frontlight comprises a lightguide disposed to receive light from a blue or UV light emitting source and further comprises a region comprising a wavelength conversion material such as a phosphor film. In another embodiment, the backlight comprises 3 layers of film lightguides wherein each lightguide illuminates a display with substantially uniform luminance when the corresponding light source is turned on. In this embodiment, the color gamut can be increased by reducing the requirements of the color filters and the display can operate in a color sequential mode or all-colors-on simultaneously mode. In a further embodiment, the backlight or frontlight comprises 3 layers of film lightguides with 3 spatially distinct light emitting regions comprising light extraction features wherein each light extraction region for a particular lightguide corresponds to a set of color pixels in the display. In this embodiment, by registering the light extracting features (or regions) to the corresponding red, green, and blue pixels (for example) in a display panel, the color filters are not necessarily needed and the display is more efficient. In this embodiment, color filters may be used, however, to reduce crosstalk.

In a further embodiment, the light emitting device comprises a plurality of lightguides (such as a red, green and blue lightguide) disposed to receive light from a plurality of light sources emitting light with different wavelength spectrums (and thus different colored light) and emit the light from substantially different regions corresponding to different colored sub-pixels of a spatial light modulator (such as an LCD panel), and further comprises a plurality of light redirecting elements disposed to redirect light from the lightguides towards the spatial light modulator. For example, each lightguide may comprise a cladding region between the lightguide and the spatial light modulator wherein light redirecting elements such as microlenses are disposed between the light extraction features on the lightguide and the spatial light modulator and direct the light toward the spatial light modulator with a FWHM of less than 60 degrees, a FWHM of less than 30 degrees, an optical axis of emitted light within 50 degrees from the normal to the spatial light modulator output surface, an optical axis of emitted light within 30 degrees from the normal to the spatial light modulator output surface, or an optical axis of emitted light within 10 degrees from the normal to the spatial light modulator output surface. In a further embodiment, an arrangement of light redirecting elements are disposed within a region disposed between the plurality of lightguides and the spatial light modulator to reduce the FWHM of the light emitted from the plurality of lightguides. The light redirecting elements arranged within a region, such as on the surface of a film layer, may have similar or dissimilar light redirecting features.

In another embodiment, a backlight or frontlight comprises at least one light source, light input coupler, and lightguide wherein lightguide forms a substrate or protective region within the display panel. In one embodiment, the lightguide is the substrate for the liquid crystal display. In a further embodiment, the lightguide is optically coupled to an outer surface of the display, is disposed within the display, within the liquid crystal cell, or in-between two substrates of the display.

In another embodiment, a backlight or frontlight comprises at least one light source and a light input coupler comprising at least one coupling lightguide optically coupled to at least one display component (such as a substrate, film, glass, polymer or other layer of a liquid crystal based display or other display) wherein the component guides light received from the at least one coupling lightguide in a waveguide condition. By optically coupling the coupling lightguides to a display component such as an LCD glass substrate for example, the component can function as the lightguide and alleviate the need for additional backlighting films or components.

In another embodiment, a light emitting device comprises more than one lightguide or lightguide region to provide redundancy of light output in case of difficulties with one backlight or for increased light output. In military and critical display applications (such as surgery rooms), one often desires to have redundancy in case of electrical or light source or other component failure. The reduced thickness of the film based lightguide in embodiments allow for one or more additional backlights which may include more than one additional light source and driver and electronic control circuitry. In a further embodiment, one or more photodetectors such as silicon photodiodes or LEDs used in “reverse mode” detects the light intensity (or color) of the light within a region to determine if the redundant lightguide, color compensation lightguide, or high brightness backlight lightguide should be turned on. In another embodiment, multiple LEDs driven from the same or different circuits may be used at the same or different light input couplers to provide redundancy (or color compensation, or high brightness mode) within a single light input coupler or redundancy through multiple light input couplers within the same lightguide. When using multiple light input couplers on the same lightguide, the couplers may be arranged on the same side, the opposite side, an orthogonal side, or at an edge different to the first light input coupler.

Modes of the Light Emitting Device

In another embodiment, a light emitting device comprises one or more modes selected from the group: normal viewing mode, daytime viewing mode, high brightness mode, low brightness mode, nighttime viewing mode, night vision or NVIS compatible mode, dual display mode, monochrome mode, grayscale mode, transparent mode, full color mode, high color gamut mode, color corrected mode, redundant mode, touchscreen mode, 3D mode, field sequential color mode, privacy mode, video display mode, photo display mode, alarm mode, nightlight mode, and emergency lighting/sign mode

Frontlight Light Emitting Device

In one embodiment, the light emitting device emits light toward a display with reflective components such that the display is frontlit. In another embodiment, a display comprises a film based light emitting device comprising a light source, light input coupler, and lightguide lighting a display from the front wherein the light extracting regions of the lightguide direct light toward an interferometric modulator. The lightguide may be a component external to the display, an integral component of the display, or optical coupled to a surface or layer of the display.

In another embodiment, a display comprises a film based light emitting device comprising a light source, light input coupler, and lightguide lighting a display from the front wherein the light extracting regions of the lightguide direct light toward at least one selected from the group: a reflective LCD, electrophoretic display, cholesteric display, zenithal bistable device, reflective LCD, electrostatic display, electrowetting display, bistable TN displays, micro-cup EPD displays, grating aligned zenithal display, photonic crystal display, electrofluidic display, and electrochromic displays, and a time-multiplexed optical shutter display.

Flexible Backlight or Frontlight

In another embodiment, a display comprises a film based light emitting device comprising a light source, light input coupler, and lightguide wherein the lightguide. lightguide region, or coupling lightguides can be bent or folded to radius of curvature of less than 75 times the thickness of lightguide or lightguide region and function similarly to similar lightguide or lightguide region that has not been similarly bent. In another embodiment, the lightguide, coupling lightguide, or lightguide region can be bent or folded to radius of curvature greater than 10 times the times the thickness lightguide or lightguide region and function similarly to similar lightguide or lightguide region that has not been similarly bent.

In another embodiment, the backlight or frontlight is incorporated into a portable device such as a cellphone, smartphone, pda, laptop, ebook, e-reader, or other computing device.

Luminance Uniformity of the Backlight, Frontlight, or Light Emitting Device

In one embodiment, a light emitting device comprises a light source, a light input coupler, and a film-based lightguide wherein the 9-spot spatial luminance uniformity of the light emitting surface the light emitting device measured according to VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001 is greater than one selected from the group: 60%, 70%, 80%, 90%, and 95%. In another embodiment, a display comprises a spatial light modulator and a light emitting device comprising a light source, a light input coupler, and a film-based lightguide wherein the 9-spot spatial luminance uniformity of the light reaching the spatial light modulator (measured by disposing a white reflectance standard surface such as Spectralon in the location where the spatial light modulator would be located to receive light from the lightguide and measuring the light reflecting from the standard surface in 9-spots according to VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001) is greater than one selected from the group: 60%, 70%, 80%, 90%, and 95%. In another embodiment, a display comprises a spatial light modulator and a light emitting device comprising a light source, a light input coupler, and a film-based lightguide wherein the 9-spot spatial luminance uniformity of the display measured according to VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001) is greater than one selected from the group: 60%, 70%, 80%, 90%, and 95%.

Color Uniformity of the of the Backlight, Frontlight, or Light Emitting Device

In one embodiment, a light emitting device comprises a light source, a light input coupler, and a film-based lightguide wherein the 9-spot sampled spatial color non-uniformity, Δu′v′, of the light emitting surface of the light emitting device measured on the 1976 u′, v′ Uniform Chromaticity Scale as described in VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001 (Appendix 201, page 249) is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004 when measured using a spectrometer based spot color meter. In another embodiment, a display comprises a spatial light modulator and a light emitting device comprising a light source, a light input coupler, and a film-based lightguide wherein the 9-spot sampled spatial color non-uniformity, Δu′v′, of the of the light reaching the spatial light modulator (measured by disposing a white reflectance standard surface such as Spectralon in the location where the spatial light modulator would be located to receive light from the lightguide and measuring the color of the standard surface on the 1976 u′, v′Uniform Chromaticity Scale as described in VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001 (Appendix 201, page 249) is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004 when measured using a spectrometer based spot color meter. In another embodiment, a display comprises a spatial light modulator and a light emitting device comprising a light source, a light input coupler, and a film-based lightguide wherein the 9-spot sampled spatial color non-uniformity, Δu′v′, of the display measured on the 1976 u′, v′ Uniform Chromaticity Scale as described in VESA Flat Panel Display Measurements Standard version 2.0, Jun. 1, 2001 (Appendix 201, page 249) is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004 when measured using a spectrometer based spot color meter.

Angular Profile of Light Emitting from the Light Emitting Device

In one embodiment, the light emitting from at least one surface of the light emitting device has an angular full-width at half-maximum intensity (FWHM) less than one selected from the group: 120 degrees, 100 degrees, 80 degrees, 60 degrees, 40 degrees, 20 degrees, and 10 degrees. In another embodiment, the light emitting from at least one surface of the light emitting device has at least one angular peak of intensity within at least one angular range selected from the group: 0-10 degrees, 20-30 degrees, 30-40 degrees, 40-50 degrees, 60-70 degrees, 70-80 degrees, 80-90 degrees, 40-60 degrees, 30-60 degrees, and 0-80 degrees from the normal to the light emitting surface.

Optical Redundancy

In one embodiment, the light emitting device comprises coupling lightguides which provide a system for optical redundancy. Optical redundancy provides for the ability of the device to function at acceptable illuminance uniformity, luminance uniformity, and/or color uniformity levels through multiple optical paths from different light sources that overlap in at least one region. The optical redundancy may be achieved through stacking lightguides, coupling light from more than one light source into a light input coupler, or disposing light input couplers for the same lightguide film on a plurality of sides of the lightguide (such as on opposite sides of the lightguide). More than one method of achieving optical redundancy may be employed, for example, by stacking two or more lightguides that each comprises light input couplers that are each disposed to receive light from a plurality of light sources.

In certain embodiments, optical redundancy is used to increase the spatial or angular uniformity (luminance, illuminance, and/or color), provide a combination of angular or spatial light output profiles (low angular output from one lightguide and high angular output from a second lightguide, for example), provide increased luminance levels, provide a backup light emitting region when component failure causes light from the first lightguide to fall below specification (such as color uniformity, luminance uniformity, or luminance) in the overlapping region, increase the color gamut (combining light output from white and red LEDs, for example), and/or provide color mixing (combining the output from red, green, and blue LEDs, for example).

In one embodiment, optical redundancy is used to prevent or limit the undesirable effects of light source failure or component failure (such as LED driver or a solder joint failure). For example, two lightguides may each be coupled to a separate light input coupler with separate light sources and the lightguides may be stacked in a light output direction and each lightguide independently designed with light extraction features to provide uniform output in a light emitting region. If the LED fails in the first light input coupler, the second light input coupler is operable to provide uniform light output. Similarly, if the color of the first LED within the first light input coupler changes due to temperature or degradation, the effects (color changes such as off-white) will be less due to the optical redundancy of a stacked system.

In another embodiment, the light output from two or more light sources are coupled into the light input coupler of a light emitting device comprising optical redundancy and the optical redundancy reduces the color or luminance binning requirements of the LEDs. In this embodiment, optical redundancy provides for the mixing of light from a plurality of light sources within a region (such as within the coupling lightguides) such that the color from each light source is averaged spatially with each coupling lightguide receiving light from each light source and directing the light received into the lightguide and/or light mixing region.

In another embodiment, a light emitting device comprises at least one coupling lightguide disposed to receive light from at least two light sources. The light from the at least two light sources is mixed within a first region of the at least one coupling lightguide. The first region is defined within a distance from the light emitting region of the light emitting device less than one selected from the group: 100%, 70%, 50%, 40%, 30%, 20%, 10%, and 5% of the largest dimension of the light emitting device output surface or light emitting region.

In a further embodiment, a light emitting device comprises at least one coupling lightguide disposed to receive light from at least two light sources wherein the light from the at least two light sources is mixed over the length of the at least one coupling lightguide and the light mixing region. In this embodiment, the combined length of the at least one coupling lightguide and the light mixing region in the direction of travel of light exiting the coupling lightguide is greater than one selected from the group: 100%, 70%, 50%, 40%, 30%, 20%, 10%, and 5% of the largest dimension of the light emitting device output surface or light emitting region.

In a further embodiment, a light emitting device comprising a plurality of light sources comprises optical redundancy. The device may be dimmed by adjusting the light output of one or more LEDs while leaving the output driving pattern of one or more LEDs substantially constant. For example, a light emitting device comprising a first group of LEDs, such as a first string of LEDs L1, L2, and L3 connected in an electrical series and optically coupling light into light input couplers LIC1, LIC2, and LIC3, respectively, and further comprising a second group of LEDs, such as a second string of LEDs L4, L5, and L6 connected in an electrical series and optically coupling light into light input couplers LIC1, LIC2, and LIC3, respectively, can be uniformly dimmed (dimmed while maintaining spatial luminance uniformity of the light emitting surface, for example) from, for example 50% to 100% output luminance, by adjusting the electrical current to the second string of LEDs. Similarly, the color of the light output can be uniformly adjusted by increasing or decreasing the electrical current to the second string when the color of the light output of the second string is different than the color output of the first string. Similarly, three or more groups of LEDs may be controlled independently to provide optical redundancy or uniform adjustment of the luminance or color. Three or more groups of LEDs with different colors (red, green, and blue, for example) may be adjusted independently to vary the output color while providing spatial color uniformity.

Uniformity Maintenance

In one embodiment, a first color difference Δu′v′₁ of two light sources disposed to couple light into a light input coupler is greater than the spatial color non-uniformity Δu′v′₂ of at least one selected from the group: the 9 spot sampled color non-uniformity of the light emitting region disposed to receive light from the light input coupler, the light output surface of the light emitting device, and the light exiting the coupling lightguides.

In another embodiment, a light emitting device comprises a first group of light sources comprising at least one light source and a second group of light sources comprising at least one light source. In this embodiment, at least one light source from the first group and at least one light source from the second group couple light into the same light input coupler and the 9-spot spatial color non-uniformity, Δu′v′, of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004 when measured using a spectrometer based spot color meter, and the 9-spot spatial color non-uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is less than one selected from the group: 0.2, 0.1, 0.05, 0.01, and 0.004. In another embodiment, the 9-spot spatial color non-uniformity, Δu′v′, of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is less than 0.05 and the 9-spot spatial color non-uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is less than 0.05. In a further embodiment, the 9-spot spatial color non-uniformity, Δu′v′, of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is less than 0.05 and the 9-spot spatial color non-uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is less than 0.1.

In another embodiment, a light emitting device comprises a first group of light sources comprising at least one light source and a second group of light sources comprising at least one light source. In this embodiment, at least one light source from the first group and at least one light source from the second group couple light into the same light input coupler and the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is greater than one selected from the group: 50%, 60%, 70%, 80%, and 90%, and the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is greater than one selected from the group: 50%, 60%, 70%, 80%, and 90%. In another embodiment, the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is greater than 70%, and the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is greater than 70%. In a further embodiment, the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from both the first group of light sources and the second group of light sources is greater than 80%, and the 9-spot spatial luminance uniformity of the light emitting region or the light output surface when receiving light from only the first group of light sources is greater than 70%.

Stacked Lightguides

In one embodiment, a light emitting device comprises at least one film lightguide or lightguide region disposed to receive and transmit light from a second film lightguide or lightguide region such that the light from the second lightguide improves the luminance uniformity, improves the illuminance uniformity, improves the color uniformity, increases the luminance of the light emitting region, and/or provides a back-up light emitting region when component failure causes light from the first lightguide to fall below specification (such as color uniformity, luminance uniformity, or luminance) in the overlapping region.

Plurality of Light Sources Coupling into Light Input Coupler

In another embodiment, a plurality of light sources are disposed to couple light into a light input coupler such that a portion of the light from the plurality of light sources is coupled into at least one coupling lightguide such that the light output is combined. By combining the light output from a plurality of light sources within the coupling lightguides, the light is “mixed” within the coupling lightguides and the output is more uniform in color, luminance, or both. For example, two white LEDs disposed adjacent a light input surface of a collection of coupling lightguides within a light input coupler can have substantially the same spatial luminance or color uniformity in the light emitting region if one of the light sources fails. In another embodiment, light sources emitting light of two different colors are disposed to couple light into the same light input coupler. In this embodiment, the light input coupler provides the mixing within the coupling lightguides, and furthermore, the coupling lightguides provide optical redundancy in case one light source fails. The optical redundancy improves the color uniformity when light sources of two or more colors are coupled into the same light input coupler. For example, three white LEDs, each with different color temperatures, may be coupled into the same light input coupler. If one of the LEDs fails, the light output from the other two LEDs is still mixed and provides more uniformity than single LEDs with different color outputs coupled into two adjacent light input couplers. In one embodiment, a light source comprises a plurality of LED chips, such as at least one selected from the group: 3, 5, 10, 15, 20, 25, and 30 LED chips disposed in an array or arrangement to couple light into a single light input coupler. In one embodiment, a light source comprises a plurality of LED chips, such as at least one selected from the group: 3, 5, 10, 15, 20, 25, and LED chips disposed in an array or arrangement to couple light into more than one light input coupler. In a further embodiment a light source disposed to couple light into a light input coupler comprises a plurality of LED chips with a light emitting surface area with a light emitting dimension less than one selected from the group: 0.25 millimeters, 0.3 millimeters, 0.5 millimeters, 0.7 millimeters, 1 millimeter, 1.25 millimeters, 1.5 millimeters, 2 millimeters, and 3 millimeters.

Light Input Couplers on Different Sides of the Lightguide

In another embodiment, a plurality of light input couplers are disposed on two or more edge regions of a lightguide wherein the optical axes of the light exiting the coupling lightguides are oriented at an angle greater than 0 degrees to each other. In a further embodiment, the light input couplers are disposed on opposite or adjacent edges or sides of the lightguide. In one embodiment, a light emitting device comprises a plurality of light input couplers disposed on two or more edge regions of a lightguide and the luminance or color uniformity of the light emitting region is substantially the same when the light output of the first light input coupler is increased or decreased relative to the light output of the second light input coupler. In one embodiment, the light extraction features are disposed within the light emitting region such that the spatial luminance uniformity is greater than 70% when receiving light from only the first light input coupler and the spatial luminance uniformity is greater than 70% when receiving light from the first light input coupler and the second light input coupler. In another embodiment, the light extraction features are disposed within the light emitting region such that the 9-spot spatial color non-uniformity is less than 0.01 when receiving light from only the first light input coupler and the 9-spot spatial color non-uniformity is less than 0.01 when receiving light from the first light input coupler and the second light input coupler.

Applications of the Light Emitting Device

Because the embodiments described herein enable inexpensive coupling into thin films, there are many general illumination and backlighting applications. The first example is general home and office lighting using roll-out films on walls or ceiling. Beyond that, the film can bend to shape to non-planar shapes for general illumination. Additionally, it can be used as the backlight or the frontlight in the many thin displays that have been or are being developed.

The light emitting device of one embodiment can be used for backlighting or frontlighting purposes in passive displays, e.g., as a backlight or frontlight for an illuminated advertising poster, as well as for active (changing) displays such as LCD displays. Suitable displays include, but are not limited to, mobile phone displays, mobile devices, aircraft display, watercraft displays, televisions, monitors, laptops, watches (including one where the band comprises a flexible lightguide which is capable of illumination or “lighting up” in a predetermined pattern by an LED within the watch or watch band), signs, advertising displays, window signs, transparent displays, automobile displays, electronic device displays, and other devices where LCD displays are known to be used.

Some applications generally require compact, low-cost white-light illumination of consistent brightness and color across the illuminated area. It is cost-effective and energy-efficient to mix the light from red, blue, and green LEDs for this purpose, but color mixing is often problematic. However, with some embodiments, light from red, blue, and green light sources can all be input into each stack of legs/input areas, and by the time the light reaches the sheet, it will be sufficiently mixed that it appears as white light when it exits the light emitting region of the lightguide. The light sources can be geometrically situated, and adjusted in intensity, to better provide uniform intensities and colors across the lightguide. A similar arrangement can be attained by providing stacked sheets (more specifically stacked sheet bodies or lightguides) wherein the colors in the sheets combine to provide white light. Since some displays are provided on flexible substrates—for example, electronic ink thin-film displays on printed pages—the sheets provide a means for allowing backlighting while maintaining the flexibility of the display's media.

Method of Manufacturing Light Input/Output Coupler

In one embodiment, the lightguide and light input or output coupler are formed from a light transmitting film by creating segments of the film corresponding to the coupling lightguides and translating and bending the segments such that a plurality of segments overlap. In a further embodiment, the input surfaces of the coupling lightguides are arranged to create a collective light input surface by translation of the coupling lightguides to create at least one bend or fold.

In another embodiment, a method of manufacturing a lightguide and light input coupler comprising a light transmitting film with a lightguide region continuously coupled to each coupling lightguide in an array of coupling lightguides, said array of coupling lightguides comprising a first linear fold region and a second linear fold region, comprises the steps: (a) increasing the distance between the first linear fold region and the second linear fold region of the array of coupling lightguides in a direction perpendicular to the light transmitting film surface at the first linear fold region; (b) decreasing the distance between the first linear fold region and the second linear fold region of the array of coupling lightguides in a direction substantially perpendicular to the first linear fold region and parallel to the light transmitting film surface at the first linear fold region; (c) increasing the distance between the first linear fold region and the second linear fold region of the array of coupling lightguides in a direction substantially parallel to the first linear fold region and parallel to the light transmitting film surface at the first linear fold region; decreasing the distance between the first linear fold region and the second linear fold region of the array of coupling lightguides in a direction perpendicular to the light transmitting film surface at the first linear fold region; (d) such that the coupling lightguides are bent, disposed substantially one above another, and aligned substantially parallel to each other. These steps (a), (b), (c) and (d) do not need to occur in alphabetical order and the linear fold regions may be substantially parallel.

Relative Position Maintaining Element

In one embodiment, at least one relative position maintaining element substantially maintains the relative position of the coupling lightguides in the region of the first linear fold region, the second linear fold region or both the first and second linear fold regions. In one embodiment, the relative position maintaining element is disposed adjacent the first linear fold region of the array of coupling lightguides such that the combination of the relative position maintaining element with the coupling lightguide provides sufficient stability or rigidity to substantially maintain the relative position of the coupling lightguides within the first linear fold region during translational movements of the first linear fold region relative to the second linear fold region to create the overlapping collection of coupling lightguides and the bends in the coupling lightguides.

Glass Laminate

In another embodiment, the lightguide is disposed within or on one side of a glass laminate. In another embodiment, the lightguide is disposed within a safety glass laminate. In a further embodiment, at least one selected from the group: lightguide, cladding, and adhesive layer comprises polyvinyl butyrate.

Patterned Lightguides

In another embodiment, at least one of the lightguide or coupling lightguides is a coated region disposed on a cladding, carrier film, substrate or other material. By using a coated pattern for the lightguide, different pathways for the light can be achieved for light directed into the coupling lightguides or lightguide. In one embodiment, the lightguide region comprises lightguide regions which direct light to separate light emitting regions wherein the neighboring lightguide regions with light extracting features emit light of a different color.

Light Extraction Features

In one embodiment, the light extraction features are disposed on or within a film, lightguide region or cladding region by embossing or employing a “knurl roll” to imprint surface features on a surface. In another embodiment, the light extraction features are created by radiation (such as UV exposure) curing a polymer while it is in contact with a drum, roll, mold or other surface with surface features disposed thereon. In another embodiment, light extraction features are formed in regions where the cladding or low refractive index material or other material on or within the lightguide is removed or formed as a gap. In another embodiment, the lightguide region comprises a light reflecting region wherein light extraction features are formed where the light reflecting region is removed. Light extraction may comprise or be modified (such as the percent of light reaching the region that is extracted or direction profile of the extracted light) by adding scattering, diffusion, or other surface or volumetric prismatic, refracting, diffracting, reflecting, or scattering elements within or adjacent the light extraction features or regions where the cladding or other layer has been removed.

In one embodiment, the light extraction features comprise an ink or material within a binder comprising least one selected from the group: titanium dioxide, barium sulfate, metal oxides, microspheres or other non-spherical particles comprising polymers (such as PMMA, polystyrene), rubber, and other inorganic materials.

In another embodiment, the light extraction features are formed by removing or altering the surface by one selected from the group: mechanical scribing, laser scribing, laser ablation, surface scratching, stamping, hot stamping, sandblasting, radiation exposure, ion bombardment, solvent exposure, material deposition, etching, solvent etching, plasma etching, and chemical etching.

In another embodiment, more than one light extraction layer or region comprising light extraction features is used and the light extraction layer or region may be located on one surface, two surfaces, within the volume, within multiple regions of the volume, or a combination of the aforementioned locations within the film, lightguide, lightguide region, cladding, or a layer or region disposed on or within the lightguide.

Folding and Assembly

In one embodiment, the coupling lightguides are heated to soften the lightguides during the folding or bending step. In another embodiment, the coupling lightguides are folded while they are at a temperature above one selected from the group: 50 degrees Celsius, 70 degrees Celsius, 100 degrees Celsius, 150 degrees Celsius, 200 degrees Celsius, and 250 degrees Celsius.

The following are more detailed descriptions of various embodiments illustrated in the Figures.

FIG. 1 is a top view of one embodiment of a light emitting device 100 comprising a light input coupler 101 disposed on one side of a film-based lightguide. The light input coupler 101 comprises coupling lightguides 104 and a light source 102 disposed to direct light into the coupling lightguides 104 through a light input surface 103 comprising one or more input edges of the coupling lightguides 104. In one embodiment, each coupling lightguide 104 includes a coupling lightguide terminating at a bounding edge. Each coupling lightguide is folded such that the bounding edges of the coupling lightguides are stacked to form the light input surface 103. The light emitting device 100 further comprises a lightguide region 106 comprising a light mixing region 105, a lightguide 107, and a light emitting region 108. Light from the light source 102 exits the light input coupler 101 and enters the lightguide region 106 of the film. This light spatially mixes with light from different coupling lightguides 104 within the light mixing region 105 as it propagates through the lightguide 107. In one embodiment, light is emitted from the lightguide 107 in the light emitting region 108 due to light extraction features (not shown).

FIG. 2 is a perspective view of one embodiment of a light input coupler 200 with coupling lightguides 104 folded in the −y direction. Light from the light source 102 is directed into the light input surface 103 comprising input edges 204 of the coupling lightguides 104. A portion of the light from the light source 102 propagating within the coupling lightguides 104 with a directional component in the +y direction will reflect in the +x and −x directions from the lateral edges 203 of the coupling lightguides 104 and will reflect in the +z and −z directions from the top and bottom surfaces of the coupling lightguides 104. The light propagating within the coupling lightguides is redirected by the folds 201 in the coupling lightguides 104 toward the −x direction.

FIG. 3 is a top view of one embodiment of a light emitting device 300 with three light input couplers 101 on one side of the lightguide region 106 comprising the light mixing region 105, a lightguide 107, and the light emitting region 108.

FIG. 4 is a top view of one embodiment of a light emitting device 400 with two light input couplers 101 disposed on opposite sides of the lightguide 107. In certain embodiments, one or more input couplers 101 may be positioned along one or more corresponding sides of the lightguide 107.

FIG. 5 is a top view of one embodiment of a light emitting device 500 with two light input couplers 101 disposed on the same side of the lightguide region 106. The light sources 102 are oriented substantially with the light directed toward each other in the +y and −y directions.

FIG. 6 is a cross-sectional side view of one embodiment of a light emitting device 600 defining a region 604 near a substantially planar light input surface 603 comprised of planar edges of coupling lightguides 104 disposed to receive light from a light source 102. The coupling lightguides comprise core regions 601 and cladding regions 602. A portion of the light from the light source 102 input into the core region 601 of the coupling lightguides 104 will totally internally reflect from the interface between the core region 601 and the cladding region 602 of the coupling lightguides 104. In the embodiment shown in FIG. 6, a single cladding region 602 is positioned between adjacent core regions 601. In another embodiment, two or more cladding regions 602 are positioned between adjacent core regions 601.

FIG. 7 is a top view of one embodiment of a light emitting backlight 1000 configured to emit red, green, and blue light. The light emitting backlight 1000 includes a red light input coupler 1001, a green light input coupler 1002, and a blue light input coupler 1003 disposed to receive light from a red light source 1004, a green light source 1005, and a blue light source 1006, respectively. Light from each of the light input couplers 1001, 1002, and 1003 is emitted from the light emitting region 108 due to the light extraction features 1007 which redirect a portion of the light to angles closer to the surface normal within the lightguide region 106 such that the light does not remain within the lightguide 107 and exits the light emitting device 1000 in a light emitting region 108. The pattern of the light extraction features 1007 may vary in one or more of size, space, spacing, pitch, shape, and location within the x-y plane or throughout the thickness of the lightguide in the z direction.

FIG. 8 is a cross-sectional side view of one embodiment of a light emitting device 1100 comprising the light input coupler 101 and the lightguide 107 with a reflective optical element 1101 disposed adjacent a the cladding region 602 and a light source 1102 with an optical axis in the +y direction disposed to direct light into the coupling lightguides 104. Light from the light source 1102 propagates through the coupling lightguides 104 within the light input coupler 101 and through the light mixing region 105 and the light output region 108 within the lightguide region 106. Referring to FIG. 8, a first portion of light 1104 reaching the light extraction features 1007 is redirected toward the reflecting optical element 1101 at an angle less than the critical angle such that it can escape the lightguide 107, reflect from the reflective optical element 1101, pass back through the lightguide 107, and exit the lightguide 107 through the light emitting surface 1103 of the light emitting region 108. A second portion of light 1105 reaching the light extraction features 1007 is redirected toward the light emitting surface 1103 at an angle less than the critical angle, escapes the lightguide 107, and exits the lightguide 107 through the light emitting surface 1103 of the light emitting region 108.

FIG. 9 is a cross-sectional side view of one embodiment of a light emitting display 1200 illuminated by a red lightguide 1201, a green lightguide 1202, and a blue lightguide 1203.

The locations of the pixels of the display panel 1204 with corresponding red pixels 12010, green pixels 1209, and blue pixels 1208 correspond to light emitting regions of the lightguide separated by color. In this embodiment, the light extracting features 1205 within the red lightguide 1201 substantially correspond in the x-y plane to the red pixels 1210 of the display panel 1204 driven to display red information. Similarly, the green light extracting features 1206 within the green lightguide 1202 and the blue light extracting features 1207 within the blue lightguide 1203 substantially correspond in the x-y plane to the green pixels 1209 and the blue pixels 1208, respectively, of the display panel 1204 driven to display corresponding green and blue information. In another embodiment, the display panel 1204 is a spatial light modulator such as a liquid crystal panel, electrophoretic display, MEMS-based display, ferroelectric liquid crystal panel, or other spatial light modulating device such as known in the display industry. In another embodiment, the display panel 1204 further comprises color filters within the pixel regions to further reduce crosstalk from lightguide illumination reaching the pixel from neighboring light extracting features. In another embodiment, the lightguides are optically coupled to each other and the reflecting optical element is a specularly reflecting optical element. In a further embodiment, the liquid crystal panel is a transparent LCD (such as a vertical alignment type from Samsung Electronics with a transparent cathode) and there is no reflecting optical element on the opposite side of the lightguides than the display panel. In this embodiment, the display and backlight are substantially transparent and “see-through” with an ASTM D1003 total luminous transmittance greater than one selected from the group: 20%, 30%, 40%, and 50%.

FIG. 10 is a cross-sectional side view of one embodiment of a color sequential display 1300 comprising a color sequential display panel 1301 and a red, green, and blue color sequential light emitting backlight 1302 comprising a film-based lightguide. In this embodiment, red, green, and blue light from red, green and blue light sources (not shown in FIG. 13) is coupled into the lightguide through one or more light input couplers (not shown in FIG. 13). The light sources are driven in a color sequential mode and the pixel regions of the display panel 1301 are switched accordingly to display the desired color information. In one embodiment, the display panel 1301 is a spatial light modulator without color filters.

FIG. 11 is a cross-sectional side view of one embodiment of a spatial display 1400 comprising a spatial light modulator 1401 and a film-based backlight 1402 emitting light from light sources of different colors. In one embodiment, the spatial display is a liquid crystal display. In another embodiment, the spatial light modulator is a liquid crystal panel.

In a further embodiment, the film-based backlight emits light from one selected from the group: red, green, and blue; white and red; red, green, blue, and yellow; red, green, blue, yellow, and cyan; and cyan, yellow, and magenta.

FIG. 12 is a cross-sectional side view of one embodiment of a spatial display 2000 with a rear polarizer 2002 of a liquid crystal display panel 2001 optically coupled to a film-based lightguide backlight 1402 using an optical adhesive 801. The liquid crystal display panel 2001 further comprises two display substrates 2003 (glass or a polymer film for example), liquid crystal material 2004, and a front polarizer 2005. The liquid crystal display panel may further comprise one or more of the following: other suitable films, materials and/or layers such as compensation films, alignment layers, color filters, coatings, transparent conductive layers, TFTs, anti-glare films, anti-reflection films, etc. as is commonly known in the display industry.

FIG. 13 is a cross-sectional side view of a region of one embodiment of a light emitting device 2500 comprising a stack of coupling lightguides 104 disposed adjacent a light source 102 with a substrate 2502 and a collimating optical element 2501. In one embodiment, the collimating optical element 2501 is a lens which refracts and totally internally reflects light to collimate light from a light emitting diode.

FIG. 14 is a top view of a further embodiment of an input coupler and lightguide 3100 with coupling lightguides 104 wherein the array of coupling lightguides 104 has non-parallel regions. In the embodiment illustrated in FIG. 31, the coupling lightguides 104 have tapered region 3101 comprising light collimating edges 3181 and linear fold regions 2902 substantially parallel to each other. In another embodiment, the coupling lightguides 104 have non-constant separations. In another embodiment, a method for manufacturing a lightguide 3100 with coupling lightguides 104 having a tapered regions 3101 of the coupling lightguides 104 includes cutting the coupling lightguides in regions 3103 disposed at or near the tapered region 3101 such that when the array of coupling lightguides 104 are folded, the coupling lightguides 104 overlap to form a profiled, non-planar input surface that is capable of redirecting light input through the light input surface so that the light is more collimated. In another embodiment, the coupling lightguides 104 are not substantially parallel such that the coupling lightguides 104 have regions with angles between the edges that vary by more than about 2 degrees.

FIG. 15 is an angled top view of the input coupler and lightguide 3100 of FIG. 14 where the coupling lightguides 104 have been cut in regions 3103 (FIG. 14) disposed near the tapered 3101 region and folded such that they overlap to form profiled coupling lightguides 104 that are capable of redirecting light input through the light input surfaces 103 so that the light is more collimated within the coupling lightguides 104.

FIG. 16 is a cross-sectional side view of one embodiment of a light emitting device 4400 with optical redundancy comprising two lightguides 107 stacked in the z direction. Light sources and coupling lightguides within the holders 4402 arranged substantially adjacent in the y direction direct light into core regions 601 such that light 4401 is output from the light emitting region 108 from each lightguide 107.

FIG. 17 is a cross-sectional side view of one embodiment of a light emitting device 4500 with a first light source 4501 and a second light source 4502 thermally coupled to a first thermal transfer element 4505 (such as a metal core printed circuit board (PCB)) and thermally insulated (physically separated by an air gap in the embodiment shown) from a second thermal transfer element 4506 that is thermally coupled to a third light source 4503 and a fourth light source 4504. The first light source 4501 and the third light source 4503 are disposed to couple light into a first light input coupler 4507 and the second light source 4502 and the fourth light source 4504 are disposed to couple light into a second light input coupler 4508. In this embodiment, the heat dissipated from the first light source 4501 is dissipated along the first thermal transfer element 4505 in the x direction toward the second light source 4502 such that heat from the first light source 4501 does not substantially increase the temperature at the third light source 4503 by conduction.

FIG. 18 is a top view of one embodiment of a light emitting device 4600 comprising a plurality of coupling lightguides 104 with a plurality of first reflective surface edges 3906 and a plurality of second reflective surface edges 3907 within each coupling lightguide 104. In the embodiment shown in FIG. 18, three light sources 102 are disposed to couple light into respective light input edges 204 at least partially defined by respective first reflective surface edges 3906 and second reflective surface edges 3907. The lightguide 107 and the coupling lightguides 104 are designed such that the light emitting device 4600 has a VESA 9-spot sampled spatial luminance uniformity in the light emitting area 108 greater than 70% when illuminated by only one, two, or three of the light sources 102 disposed to couple light into the light input edges 204 of the coupling lightguides 104. When the light sources 102 are different colors, the light emitting device 4600 has a VESA 9-spot sampled spatial color non-uniformity, Δu′v′, in the light emitting area 108 less than 0.2 when illuminated by only one, two, or three of the light sources 102 disposed to couple light into the light input edges 204 of the coupling lightguides 104.

FIG. 19 is an enlarged perspective view of the coupling lightguides 104, as indicated at A in FIG. 18, with the light input edges 204 disposed between the first reflective surface edges 3906 and the second reflective surface edges 3907. The light sources 102 are omitted in FIG. 19 for clarity.

FIG. 20 is a cross-sectional side view of the coupling lightguides 104 and the light source 102 of one embodiment of a light emitting device 4800 comprising index matching regions 4801 disposed between the core regions 601 of the coupling lightguides 104 in the index-matched region 4803 of the coupling lightguides 104 disposed proximate the light source 102. The light source 102 is positioned adjacent the coupling lightguides 104 and the high angle light 4802 from the light source 102 propagates through the coupling lightguides 104 and the index matching region 4801 and is coupled into the coupling lightguides 104 at a location distant from the light input edge 204 of the coupling lightguides 104. In the embodiment shown in FIG. 20, the light from the light source 102 is coupled into more coupling lightguides because the light, for example at 60 degrees from the optical axis 4830 of the light source 102 propagates into a core region 601 near the light source, propagates through the index matching region 4801, and totally internally reflects in a core region 601 further away from the light source 102. In this embodiment, a portion of the light is coupled into the outer coupling lightguides 104 that would not normally receive the light if there were cladding present at or near the light input edge 204.

EXAMPLES

Certain embodiments are illustrated in the following example(s). The following examples are given for the purpose of illustration, but not for limiting the scope or spirit of the invention.

In one embodiment, coupling lightguides are formed by cutting strips at one or more ends of a film which forms coupling lightguides (strips) and a lightguide region (remainder of the film). On the free end of the strips, the strips are bundled together into an arrangement much thicker than the thickness of the film itself. On the other end, they remain physically and optically attached and aligned to the larger film lightguide. The film cutting is achieved by stamping, laser-cutting, mechanical cutting, water jet cutting, local melting or other film processing methods. Preferably the cut results in an optically smooth surface to promote total internal reflection of the light to improve light guiding through the length of the strips. A light source is coupled to the bundled strips. The strips are arranged so that light propagates through them via total internal reflection and is transferred into the film lightguide portion. The bundled strips form a light input edge having a thickness much greater than the film lightguide region. The light input edge of the bundled strips defines a light input surface to facilitate more efficient transfer of light from the light source into the lightguide, as compared to conventional methods that couple to the edge or top of the film. The strips can be melted or mechanically forced together at the input to improve coupling efficiency. If the bundle is square shaped, the length of one of its sides I, is given by I˜√(w×t) where w is the total width of the lightguide input edge and t is the thickness of the film. For example, a 0.1 mm thick film with 1 m edge would give a square input bundle with dimensions of 1 cm×1 cm. Considering these dimensions, the bundle is much easier to couple light into compared to coupling along the length of the film when using typical light sources (e.g. incandescent, fluorescent; metal halide, xenon and LED sources). The improvement in coupling efficiency and cost is particularly pronounced at film thicknesses below 0.25 mm, because that thickness is approximately the size of many LED and laser diode chips. Therefore, it would be difficult and/or expensive to manufacture micro-optics to efficiently couple light into the film edge from an LED chip because of the étendue and manufacturing tolerance limitations. Also, it should be noted that the folds in the slots are not creases but rather have some radius of curvature to allow effective light transfer. Typically the fold radius of curvature will be at least ten times the thickness of the film.

An example of one embodiment that can be brought to practice is given here. The assembly starts with 0.25 mm thick polycarbonate film that is 40 cm wide and 100 cm long. A cladding layer of a lower refractive index material of approximately 0.01 mm thickness is disposed on the top and bottom surface of the film. The cladding layer can be added by coating or co-extruding a material with lower refractive index onto the film core. One edge of the film is mechanically cut into 40 strips of 1 cm width using a sharp cutting tool such as a razor blade. The edges of the slots are then exposed to a flame to improve the smoothness for optical transfer. The slots are combined into a bundle of approximately 1 cm×1 cm cross-section. To the end of the bundle a number of different types of light sources can be coupled (e.g. xenon, metal halide, incandescent, LED or laser). Light propagates through the bundle into the film and out of the image area. Light may be extracted from the film lightguide by laser etching into the film, which adds a surface roughness that results in frustrated total internal reflectance. Multiple layers of film can be combined to make multi-color or dynamic signs.

An example of one embodiment that has been brought to practice is described here. The apparatus began with a 381 micron thick polycarbonate film which was 457 mm wide and 762 mm long. The 457 mm edge of the film is cut into 6.35 mm wide strips using an array of razor blades. These strips are grouped into three 152.4 mm wide sets of strips, which are further split into two equal sets that were folded towards each other and stacked separately into 4.19 mm by 6.35 mm stacks. Each of the three pairs of stacks was then combined together in the center in the method to create a combined and singular input stack of 8.38 mm by 6.35 mm size. An LED module, MCE LED module from Cree Inc. (Durham, N.C., USA), is coupled into each of the three input stacks. Light emitted from the LED enters the film stack with an even input, and a portion of this light remains within each of the 15 mil strips via total internal reflections while propagating through the strip. The light continues to propagate down each strip as they break apart in their separate configurations, before entering the larger lightguide. Furthermore, a finned aluminum heat sink was placed down the length of each of the three coupling apparatuses to dissipate heat from the LED. This assembly shows a compact design that can be aligned in a linear array, to create uniform light.

A method to manufacture one embodiment of a backlight comprising three film-based lightguides is as follows. Three layers of thin film lightguides (<250 microns) are laminated to each other with a layer of lower refractive index material between them (e.g. methyl-based silicone PSA). Then, an angled beam of light, ions or mechanical substance (i.e. particles and/or fluid) patterns lines or spots into the film. If necessary, a photosensitive material should be layered on each material beforehand. The angle of the beam is such that the extraction features on the layers have the proper offset. The angle of the beam is dictated by the lightguide thickness and the width of the pixels and is given by θ=tan⁻¹(t/w), where θ is the relative angle of light to the plane of the lightguide, t is the lightguide and cladding thickness and w is the width of the pixels. Ideally the extraction features direct the light primarily in a direction toward the intended pixel to minimize cross-talk.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of the invention. Various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention. Other aspects, advantages, and modifications are within the scope of the invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. Unless indicated to the contrary, all tests and properties are measured at an ambient temperature of 25 degrees Celsius or the environmental temperature within or near the device when powered on (when indicated) under constant ambient room temperature of 25 degrees Celsius. 

What is claimed is:
 1. An optically redundant light emitting device comprising: a. a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film wherein each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides; b. a first group of light sources comprising at least one light source positioned to emit light into the stacked array of coupling lightguides; and c. a second group of light sources comprising at least one light source positioned to emit light into the stacked array of coupling lightguides, wherein: i) when the first group of light sources and the second group of light sources are emitting light, each coupling lightguide in the stacked array of coupling lightguides receives light emitted from the first group of light sources and light emitted from the second group of light sources, the light travels by total internal reflection through the light transmitting film to the light emitting area, the light emitted from the first group of light sources and the light emitted from the second group of light sources exit the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial luminance uniformity greater than 70%; and ii) when the first group of light sources is emitting light and the second group of light sources is not emitting light, the light emitted from the first group of light sources exits the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial luminance uniformity greater than 70%.
 2. The light emitting device of claim [5] wherein at least one of the first group of light sources and the second group of light sources comprises at least two light emitting diodes.
 3. The light emitting device of claim 2 wherein the first group of light sources and the second group of light sources are positioned to form a linear array of light sources.
 4. The light emitting device of claim [5] wherein the first group of light sources and the second group of light sources each comprises at least two light emitting diodes.
 5. The light emitting device of claim [5] wherein the first group of light sources has a first color temperature and the second group of light sources has a second color temperature different than the first color temperature.
 6. The light emitting device of claim [5] wherein at least one of the light emitted from the first group of light sources and the light emitted from the second group of light sources has an angular light output profile with an angular full-width at half maximum intensity less than 80 degrees.
 7. The light emitting device of claim [5] wherein the first group of light sources and the second group of light sources comprise light emitting diodes from different luminance bins.
 8. The light emitting device of claim [5] wherein: a. when the first group of light sources and the second group of light sources are emitting light, the light emitted from the first group of light sources and the light emitted from the second group of light sources exit the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial color non-uniformity (Δu′v′₁) less than 0.2; and b. when the first group of light sources is emitting light and the second group of light sources is not emitting light, the light emitted from the first group of light sources exits the light transmitting film in the light emitting area with a VESA 9-spot sampled spatial color non-uniformity (Δu′v′₂) less than 0.2.
 9. The light emitting device of claim 8 wherein Δu′v′₁ is less than 0.1 and Δu′v′₂ is less than 0.1.
 10. The light emitting device of claim 8 wherein the first group of light sources has a first color temperature and the second group of light sources has a second color temperature different than the first color temperature.
 11. A display comprising the light emitting device of claim [5] and a spatial light modulator operatively coupled to the light emitting device.
 12. An optically redundant light emitting device comprising: a. a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film wherein each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides; b. a first group of light sources comprising at least one light source positioned to emit light into the stacked array of coupling lightguides; and c. a second group of light sources comprising at least one light source positioned to emit light into the stacked array of coupling lightguides, wherein a first optical path of the light emitted from the first group of light sources overlaps with a second optical path of the light from the second group of light sources in each coupling lightguide.
 13. The light emitting device of claim [5] wherein the light emitting area has a VESA 9-spot sampled spatial luminance uniformity greater than 70% when the first group of light sources and the second group of light sources are emitting light and when only the first group of light sources is emitting light.
 14. The light emitting device of claim [5] wherein the first group of light sources and the second group of light sources are positioned to form a linear array of light sources.
 15. The light emitting device of claim [5] wherein the first group of light sources and the second group of light sources each comprises at least two light emitting diodes.
 16. A display comprising the light emitting device of claim [5] and a spatial light modulator operatively coupled to the light emitting device.
 17. A light emitting device comprising: a. a light transmitting film comprising an array of coupling lightguides extending from a light emitting area defined within the light transmitting film wherein each coupling lightguide of the array of coupling lightguides is bent to form a stacked array of coupling lightguides; b. a first group of light sources comprising at least one light source of a first color positioned to emit light into the stacked array of coupling lightguides; and c. a second group of light sources comprising at least one light source of a second color different from the first color positioned to emit light into the stacked array of coupling lightguides, wherein each coupling lightguide in the stacked array of coupling lightguides is positioned to receive light emitted from the first group of light sources and light emitted from the second group of light sources, and the light emitting area has a VESA 9-spot sampled spatial color non-uniformity (Δu′v′) less than 0.2 when the first group of light sources and the second group of light sources are emitting light and when only the first group of light sources is emitting light.
 18. The light emitting device of claim [7] wherein the first group of light sources and the second group of light sources each comprises white light emitting diodes.
 19. The light emitting device of claim 18 wherein the first group of light sources has a first color temperature and the second group of light sources has a second color temperature different than the first color temperature.
 20. The light emitting device of claim 19 wherein the first group of light sources and the second group of light sources comprise light emitting diodes from different color bins.
 21. A display comprising the light emitting device of claim [7] and a spatial light modulator operatively coupled to the light emitting device. 